I collect:
Old games - There are 3 pawn shops in town, and I try to hit them up every couple weeks. I've found a lot of NES and SNES games that I got rid of when I was younger, which is rad, but I'm also amassing a lot of crappy games.
Music - Not strictly CDs. I have at least 50 or 60 lbs of musical scores, viola music, other sheet music, method books, and other related things. I do have a bunch of random CDs, too. I should probably get rid of some, but meh.
Hard Drives - I now have close to a baker's dozen of 10-15 GB hard drives. Most of them were from either XBoxes that I modded for people, but I also accumulated some from old computers and "bad box" computers.