Here are mine/the ones I like from C.I.'s liner notes:

• Song from an album that you denounced as crap before ever hearing but now like
• A song with an exclamation point in the title
• A song from the top 25 on the Play Count list on your iPod
• A song released the year you turned 21 (you didn't have to know about it then necessarily)
• A song dedicated to your nemesis (or who you imagine your nemesis to be)
• A song by an artist introduced to you by an ex that you can still listen to without wanting to punch things or throw up
• A song you first knew only from seeing its video
• A really great song from a mediocre band
• A song about committing a crime
• A song from a tribute or charity album
• A song about kissing
• A good song that is on almost any jukebox in almost any bar
• A song with a year in the title
• A song about traveling
• A song that references another song by the same artist

ETA:

I like these a lot:

• Quotes another song, either in the music or words
• Makes you want to get high, drunk...
• Features a great bridge

ETA the second. A few more of my own:

• A song you think you sing really well
• Your favorite song to play air guitar to
• A song that does not feature a guitar or a piano as the main instrument

Board-related categories would be cool, too, like:

• A song that makes you think of BTVS that was never used on the show.
• A song by a band you found through the Buffistas.
• A song by a band that you could have, but didn't, write about for Lost in The Grooves.

Other suggestions:

• An upbeat song about a sad thing.
• Midnight driving in the rain music.
• A song about buildings and/or food.

I have my cross-genre cover picked out already, not that I want that to influence Corwood *g*

I would like to add

• More cowbell: A song containing that essential instrument (and maybe this is played out since iTunes did their list, but I have the perfect song!)
• Words to music: a song that was originally, or quotes heavily, a literary work. (Example: One of Many by Vic Chesnutt. Lyrics are a Stevie Smith Poem)
  
• A song you cannot not dance to.

Excellent categories!

I have my cross-genre cover picked out already

Hey, I had you in mind when I wrote it. And where's msbelle? Does she know about this?

This cracked me right up.

Will we settle on a final list of categories, or will we just pick from the vast lists being provided now?

Corwood will settle on a final list.

Excellent.

This cracked me right up.

Indie-tastic!

I *love* these categories, but the ones needing actual knowledge of music theory and/or structure may need some handholding. Could I tell you what part of any song is the bridge, without guessing? No. Unless it's the live version of "Sunkeneyed Girl," where he says "this song doesn't have a bridge."