Improvised Golems

This is a golem made out of the remains of a collapsed mineshaft, complete with broken support-beam arms and legs, and the howling souls of the miners who died trapped inside it. Also, a pissed-off zombie canary. It just goes to show that some people will make a golem out of anything."

— Collapsed mineshaft golem, Kingdom of Loathing

Crafting a proper Golem takes takes time, effort and often magical runes. However at a pinch many bad guys can take whatever is at hand, make it into a useful shape and sent it off against their enemies. Things like water, sand, dirt, snow may be used, often illustrating that the creator can easily make more if they are destroyed.

Closely linked to summoned creatures although in this case its only really the 'binding force' that has been summoned/ created.

Distinct from Golems and Snowlems in that they are (often)

Quick to assemble, almost instant in some cases.
Totally loyal.
Made from whatever is at hand.
Somewhat unreliable/unstable and not that smart.
Likely to collapse without a constant energy supply from their creators. (No Ontological Inertia)

Examples of Improvised Golems include:

Anime and Manga

Yuuri in Kyou Kara Maou sometimes summons improvised golems when he's channeling the demon king.
In The Slayers, there are spells to create these ones. "Golem", "Vu Vraimer" and "Mega Vraimer".
Corona of Magical Girl Lyrical Nanoha ViVid has her Creation spell, which allows her to instantly build her golem Goliath from out of the ground.

Literature

In the last Fablehaven book one of the obstacles faced in the Dreamstone is a statue of a warrior. The group have only a short time to sculpt themselves a "champion" from the available clay; both statues are then animated and do battle.
In Galatia in 2-D, the heroes build some golems from the contents of their pockets, including keys and a zippo lighter. Luckily, they had a lot of chewing gum to hold them together.
Judah Low from China Mieville's Iron Council can make golems out of anything. Even time.
In Jonathan Strange & Mr Norrell Strange creates several impromptu golems over the course of the book. He makes horse-shaped sand golems to tow a ship, animates a set of stained glass to put out a fire, and when the fire destroys them simply creates golems of water to throw themselves directly on the fire. It's mentioned that the Raven King used to create a huge golem out of ravens.
Starlight and Shadows Forgotten Realms trilogy by Elaine Cunningham has Liriel occasionally doing this with gems and ship figurehead, thanks to spellbooks of some unfortunate Red Mage.

Live Action TV

In the Lord Zedd era of Mighty Morphin Power Rangers, as well as the Kamdor episodes of Power Rangers Operation Overdrive, the Monster of the Week is arguably this, with everyday objects being brought to life by the Big Bad, turned into monsters, and sent to attack. Sometimes they get to be careful and smart about the choice of object, but sometimes it's a spur-of-the-moment monster creation, so you get... killer inner tubes, purses of doom with weapons made from whatever items happened to be inside, and evil brick walls. In fact, since Kamdor was usually on the move instead of sitting back in a castle, monsters were usually made in an "Oh, crap, Rangers might get the MacGuffin. Let's see, what's the nearest blue object - ah! That purse/amplifier/camera/etc!" moment. However, a computer monster was part of a Plan Zedd wishes he could have thought of.

Tabletop Games

The Dungeons & Dragons spell "Animate Objects" works like this in 2nd and 3rd edition. In contrast to creating an actual golem, which takes weeks of work and hugely expensive materials, the spell allows the caster to make a candlestick or rock sprout arms and legs and do its master's bidding. They're short-lived constructs, fragile and usually not great at fighting. On the other hand, the incident where a Big Bad was slain by a table makes for a great story to tell the grandkids.
- Forgotten Realms has some custom temporary animation spells, from several hand-out-of-the-wall (or floor) spells like "Manshoon's Xorn Talons" to creation of fake undead with) to "Skeletal Bride" (walking blob-headed skeleton corporeal enough to carry stuff, unlike mostly illusory Shadow Skeleton) to "Iron Maiden" (Battle Horror construct). Not counting various ways to animate weapons.
Mutants and Masterminds as the Animate Objects power which offers this explicitly, although part and parcel to it is that the objects do not actually gain any kind of humanoid form. Rather, you get the situations of tables rocking themselves across the room, carpets slithering, millstones rolling...
The old TSR comic book superhero game Marvel Super Heroes had superpowers that could be used this way. Animate Matter: Solid would allow a character to manipulate homogenous solid matter (even things like adamantium if the power was strong enough), and there was a power that would allow similar effects with machines (including doing things with functional machines, which was explicitly disallowed with Animate Matter).

Video Games

The necromancer in Diablo II is all over this. Aside from insta-summonable earth and blood golems, he can also make metal golems out of any equipment, which then takes on the enchantments and traits of their raw materials.
The first Boss Fight in Drakensang 2: The River of Time is against a golem made of scrap parts, including wooden planks, a chest, an anvil and several oversized sickle blades. Predictably it's extremely vulnerable to flames.
Ghostbusters, of course. Throughout the game, you'll have to contend with the likes of Book Golems, Coal Golems, Black Slime Golems, a Kitchen Golem (in the very first level, natch), and Graveyard Golems.
Kingdom of Loathing has a whole bunch of these.
Legendary features a gigantic golem made of cars, freight containers, chunks of concrete and random pieces of metal acquired from the surrounding area.
There's an DnD adventure in the Planescape setting where the players face a person with the ability to create golems out of objects at hand.
Golems in Vindictus instantly assemble a body out of surrounding debris when cast. Notably, if there isn't enough junk lying around, the golem must limp or crawl around until it can assimilate enough for a proper body.
- In the sister game Video Game/Mabinogi, golems are made of floating rocks, but the rocks are somehow "unpacked" from the golem crystal itself.

Web Comics

Dominic Deegan shows us a Improvised snow golem
One Knights of the Dinner Table strip had the players complaining about to the GM (Jonnny Kizinski) about the villain being able to assemble a golem out of components he found in a broom closet.
Hitmen for Destiny has a Maythorn experiment by starting with Play-Doh. It's loyal, but since it can't hear instructions and is from an ultra-weak material, it kills itself by trying to move.
The Beast Legion has Gorgorath who fits into this category. After being crushed his soul & body remains were linked to a giant suit of armor.

Web Original

Mr. Welch has used this several times, such as creating animated balloon animals and even Tequila Golems.

Western Animation

In a Simpsons Treehouse of Horror ep they made a Bride of Golem out of Play Dough for the real Golem Of Prague.