Literally Loving Thy Neighbor

Often in fiction the person who you have the crush on lives right next door. Comes in three types.

The protagonist and the neighbor fall in love with each other.
The protagonist loves the neighbor but they don't love the protagonist back. (Possibly because they're unaware of the crush.)
The neighbor loves the protagonist and they most likely know, but just doesn't feel the same way.

This neighborhood love interest can over lap with or be confused with the Girl Next Door who is average and wholesome femininity personified. He might not be able to resist the urge to take advantage on the situation and spy on her or he might visit her by Enter Stage Window.

Compare Childhood Friend Romance.

Examples of Literally Loving Thy Neighbor include:

Comic Books

Mary Jane was the girl next door to Peter Parker in both Spider-Man comics and the movies.
- Although it should be noted in the comics Peter was MJ's AUNT'S neighbor (still counts as she ended up living with her aunt though). Also unusually for this trope they didn't meet through being neighbors but through Peter's Aunt May's and Mary Jane's Aunt Anna's attempt to set them up. Played much straighter in the movies where MJ was Peter's neighbor since childhood.

Film

In Harold & Kumar go to White Castle Harold has a crush on his neighbor but is too shy to tell her.
The Film Noir In a Lonely Place about a romance between two neighbors after their involvement in a criminal investigation.
The Girl Next Door: Matthew Kidman looks through his bedroom window into the bedroom of the house next door. He sees the girl next door who's as sexy as can be. She sees him looking at her and comes over to talk with him about it.
Bryce moves in right across the street from Julie in Flipped. She sees him and decides that he's walking around with her first kiss. He takes the length of the movie to decide that she's kissable.
Whatever It Takes: Shane West is Jodi Lyn O'keefe's neighbor, who, after chasing the wrong girl., finally realities he had more in common with his friend, and the girl next door. Various scenes are heavily based on their balconies facing each others'
Drive Me Crazy where the protagonists are neighbors who use, then fall in love with each other.
In Sky High Layla walks over to Will's house so they can walk to the bus stop together.

Literature and Folklore

Many interpretations and reiterations of Shakespeare's Romeo and Juliet have the dueling families of the Capulets and the Montagues come from neighboring houses making the romance between Romeo and Juliet an example.
Older Than Feudalism: In The Bible, David and Bathsheeba being nearby each other (so that he could see into her bath).
Pride and Prejudice opens with Mr Bingley, a wealthy young bachelor, moving into Netherfield house in the neighbourhood of the Bennet family. His friend Mr Darcy quickly notices that Elizabeth Bennet is agreeable but not handsome enough to tempt him.

Live Action Television

That '70s Show had Eric living next to Donna. They eventually hook up and even get engage.
In Cougar Town, Jules and Grayson had Unresolved Sexual Tension in season 1; since it was resolved, in season 2, they have a full relationship.
Freddy lives across the hall from Carly in iCarly and he's loved her since the day they've met.
In Family Matters Urkel loves Laura. Laura's less than thrilled.
The How I Met Your Mother episode "The Platinum Rule" has the ultimate Girl Next Door as a potential love interest for Ted and the title refers to Barney's colorary to The Golden Rule (misinterpreted, obviously): "You can love thy neighbor, but never, ever love thy neighbor." The plot follows how not heeding this rule comes out badly for the others.
Family Ties: neighbor boy Skippy has an unrequited crush on Malorie.
Leonard (and Sheldon, surprisingly) almost immediately has a crush on their new neighbor Penny from across the hall in the pilot episode of The Big Bang Theory. The majority of the early seasons has Leonard pining for Penny; eventually, they start dating.
Lana Lang lives so close to Clark in Smallville that he can spy on her through his telescope.

Theatre

In the play Our Town, George and Emily live next door to each other.
Philia in A Funny Thing Happened on the Way to the Forum is the courtesan, who only just moved to her pimp's house a little before the show starts. She's wholesome, Hollywood Homely and actually does live next door.

Music

Taylor Swift in the music vidio of her song You Belong With Me is able to write messages and hold them up to her bedroom window to show her crush. He writes back because she's his friend.

Web Comics

Karate Bears totally have a crush on the neighbor.

Western Animation

From Johnny Test, the Test Twins are attracted to the neighbor boy Gil.
Phineas and Ferb: Isabella is attracted to Phineas, but he doesn't reciprocate, mainly because he is too young. Heavily implied to eventually become a two-way relationship in "Quantum Bungaloo".
Pebbles and Bamm-Bamm from The Flintstones grew up as next door neighbors.