Interstellar Weapon

The Interstellar equivalent of the ICBM. You fire it from a star system or from interstellar space, and it will hit a target light years away.

An Interstellar Weapon is distinct from a starship or an automated weapons platform. A starship or weapons platform goes over to the target and blows the hell out of it. An Interstellar Weapon either fires its payload from one star system, which proceeds to impact a target in another star system, or it is the payload that gets delivered from one star system to the other.

If entire wars are fought this way, you can take it as the most extreme aversion of Old School Dogfighting.

Anime & Manga

 * In Uchuu Senkan Yamato the Gamilas bombard Earth with radioactive bombs from their home planet.
 * The Backstory to Nanoha StrikerS features a brief flashback featuring interdimensional/interplanetary ICBMs.

Comic Books

 * Astonishing X-Men had an arc where a giant silver bullet was launched at Earth from some far-off alien world.
 * Green Lantern John Stewart once used his ring to create a sniper rifle, which he used to pick off an enemy on the other side of the galaxy.
 * Lensman had interdimensional PLANETS fired at fifteen times the speed of light through hyperspace. Two to crush the enemy planet and one to supernova their star for good measure. This was followed by an intergalactic combined psychic attack...which barely worked.
 * And to a lesser extent, planetary sized antimatter bombs, focusing the full output of a sun into a single beam, heavily armed planets fitted with FTL drives...
 * In Dark Empire, there's the Galaxy Gun, a massive cannon which launches incredibly destructive projectiles through hyperspace. It can destroy planets.

Film

 * Starship Troopers sees intelligent insects launch an asteroid through interstellar space to take out Buenos Aires. The book has something similar, except its version makes some actual sense.
 * Hitting Buenos Aires with an asteroid from a planet light-years away is the equivalent of hitting someone on the other side of the planet with a pebble.
 * There is some speculation that the attack on Buenos Aires was done by the humans themselves, in order to justify the war.
 * The Last Starfighter. Xur launches meteors at the Starfighter base.
 * In Farscape: The Peacekeeper Wars a is deployed.

Literature

 * In The Hitchhiker's Guide to the Galaxy, a race of nihilistic aliens builds a weapon that supposedly could destroy the rest of the universe.
 * Arguably, the Berserkers.
 * Alan Dean Foster is fond of this trope, most prominently in his Humanx Commonwealth series, which features a wide assortment of Lost Superweapons left scattered around the cosmos by various Precursors. The two greatest examples show up in the Grand Finale, Flinx Transcendent, and include a weapons platform whose Wave Motion Gun fires through subspace across galaxies, and an even bigger superweapon whose power source is a galaxy (indeed, multiple galaxies).
 * In Arthur C. Clarke's Sunstorm, the titular event is caused by a planetoid hurled across the galaxy.
 * Charles Stross' Iron Sunrise features guided, ramscoop-powered missiles designed to deter interplanetary invasions. If a planet is attacked, the missiles accelerate up to lightspeed and (eventually) hit the invaders' home planet.
 * Colin Kapp wrote at least two of these. In Patterns of Chaos, a technique for predicting the future let aliens in the Andromeda Galaxy seven hundred million years ago send sublight missiles at spots in our galaxy a few centuries from now with pinpoint accuracy, impacting close enough to the people they wanted to kill that a hand grenade would've done the job -- but they still sent planet killers. And then there was the Chaos Weapon, in the book of the same title, a Wave Motion Gun kept in another universe, which devoured entire stars for fuel.
 * In Halo, it's mentioned briefly in Ghosts of Onyx that the UNSC can send nukes through slipspace.
 * Of course, given that human slipdrives are far from being accurate (they'll send you to the right system, but that's as accurate as they get).
 * Stephen Baxter's Vacuum Diagrams contains an ICBM equivalent.
 * In the Star Wars Expanded Universe, there's Centerpoint Station. Built by the mysterious Celestials tens of thousands of years ago, it has the power to move and collapse stars across the galaxy.
 * There's also the Starlancer Project, developed during the Siege of Borleias to remotely bombard the Yuuzhan Vong command ships at Coruscant from the fortified Pyria system.
 * Also the Galaxy Gun, which fires hyperspace-capable planet-busting missiles while remaining in orbit above Byss.
 * How humanity is wiped out in the beginning of The Killing Star. Aliens who would rather not take the chance that we'd annihilate them decide to destroy us first, and they do so by launching missiles from their homeworld at the various inhabited planets of the Solar system. By the time the missiles arrive, they're moving at 92% of the speed of light, so we can't even see them coming before they impact.
 * The Genesis Wave in the Star Trek Novel Verse. Based on the genesis device from Star Trek II the Wrath of Khan, the weapon fires a reality-warping wave of energy programmed to Terraform worlds in its path - to make them resemble the homeworld of the aliens who built it. Launched from an Asteroid Thicket, it destroys/reforms several planets in the Genesis Wave series.

Live Action TV

 * Not sure if it counts, but in Stargate SG-1, one of the Goa'uld sends an asteroid bomb on a collision course with Earth. If this troper recalls correctly, it is from outside the solar system. And thus from interstellar space.
 * Also, any weapon transmitted through the Stargate is this by definition, as the Stargates are essentially interstellar delivery systems (well, wormhole generators that connect different solar systems). Especially the one that used all the Stargates in the galaxy to destroy the Replicators once and for all.
 * Doctor Who has had a few of these over the years, possibly the most famous being The Hand Of Omega which was a weapon to manipulate solar systems.
 * The Daleks' Reality Bomb which would have wipe out the entire whole of creation.
 * Both "Dreadnought" and "Warhead" of Star Trek Voyager involved warp-propelled warheads.
 * On one episode of Earth: Final Conflict, the Taelons developed a weapon that shot balls of lava from the Earth's core through the shows version of Hyperspace that could hit other planets in other solar systems.
 * Wormholes in Farscape: low-setting, shoot a chunk of a star at a spaceship or a planet you don't like. High-setting: annihilate the entire universe in a Class-Z Apocalypse with the Negative Space Wedgie to end all Negative Space Wedgies.

Video Games

 * Anacreon: Reconstruction 4021, the 1987 4X game, has "LA Ms," Long-Range Attack Missiles, which are basically interstellar nukes. They're one of the lighter weapons, but can be launched by the tens of thousands and are frequently to support the arrival of a proper attack force. Enough of them can destroy an entire fleet or scour the target world of all its defenses, both orbital and ground-based. There is no way to defend against a LAM attack. Anacreon is not a very happy game.
 * In Sins of a Solar Empire, each race has its own long-range doomsday device. Keep in mind that each of these can and usually are built in groups.
 * The TEC have the Novalith Cannon, which decimates planets.
 * The Vasari have the Kosutra Cannon, which decimates things orbiting planets.
 * The Advent have Deliverance Engines, which fire culture and propaganda.
 * One particularly "happy" strategy with the TEC Novalith is to fire it at planets that belong to your "ally". Because it takes the rounds some time to hit the planet, and because you can't see the round while it's underway (you don't even get a warning), you can pre-position your ships to attack as soon as the Novalith cannon rounds hit. This is largely considered both poor sportsmanship and exceedingly clever when pulled off properly.
 * The human Node Missiles in Sword of the Stars could be considered this, especially in the earlier versions of the game. Dozens of these could be sent to soften up enemy defenses before the arrival of the fleet. Unfortunately, later versions significantly reduced their damage and upped their cost, reducing their usefulness, especially given their slow interstellar speeds (Node Missile drives are not upgradeable).
 * They are only slow relative to the fastest available starship drives, and even then not that much slower. They are very speedy compared to drives that would be standard when you can actually research them, should you choose to make a priority of getting them.
 * One of these is used in the backstory of Mass Effect. It is used to take out a Reaper, and it grazed a planet, leaving a massive canyon/scar on the planet in question. It's theorized in the blurb that it would take a mass acceleration cannon kilometers long to create that much power. By comparison, the longest main cannon in the game series so far is half a kilometer long.
 * Technically, as described in such loving detail in Mass Effect 2, all kinetic weapons fall under this categorization, because once you fire this hunk of metal, it keeps going till it hits something. That can be a ship, or the planet behind that ship. It might go off into deep space and hit somebody else in ten thousand years. If you pull the trigger on this, you are ruining someone's day, somewhere and sometime. That is why you check your damn targets! That is why you wait for the computer to give you a damn firing solution! That is why, Serviceman Troper, we do not "eyeball it!" This is a weapon of mass destruction. You are not a cowboy shooting from the hip!
 * Ogame has interplanetary missiles that damage enemy planet's defenses (but not ships) without any chance of repair (instead of the usual 70%), though counter missiles are cheaper and available earlier.

Tabletop Games
"...can destroy 100 Solar Systems in a single move! A "small" Omega ship is 9,000 miles across! Its mere presence 10,000 light-years away constitutes an act of WAR!"
 * The Battle for Andromeda, produced by Galaxy-Foundation Games in 1976, included a type of dreadnought called the Omega ship. The game was Space Opera on a Lensman level, and an Omega ship was the Death Star on steroids, crack, PCP, and probably several other stimulants. An ad stated that it:

Webcomics

 * Schlock Mercenary has the "Discontiguous Particle Accelleration System" - beam weapon the size of a planetoid, which fires through instantaneous wormhole and can hit any place in the galaxy.

Web Original

 * The Nicoll-Dyson laser of Orion's Arm. There is also a weapon called a Killer Star, it causes a star to go supernova but in such a way that most of the energy is sent in one direction.
 * Orion's Arm has Dyson Sphere powered planet-killer beam weapons, kinetic relativistic kill vehicles aplenty, monopole-based 'conversion bombs' which can destroy stars, and more, almost always wielded by transapients. The highest Archai, however, have access to Metric Bombs, which are essentially void ships turned into weapons. They can travel across space at near the speed of light almost entirely undetected inside a void bubble, and destroy entire star systems by altering the very nature of spacetime at the heart of the central star and causing it to go supernova regardless of its mass. All that remains afterward is a black hole.

Real Life

 * Near-Earth asteroids
 * Gamma ray bursts