I unloaded a ton of RPG material a year or two ago. I just boxed it up and took it to Half-Price Books, so I got even less than I would if I had ebay'd everything off, I'm sure.
I kept all my D&D stuff (from all editions), Mutants & Masterminds, True20, Lejendary Adventure, Rolemaster/MERP, Savage Worlds, and my Call of Cthulhu stuff.
I got rid of: Top Secret SI, Morrow Project, Chill (Fasa), Star Trek (Fasa), Chivalry & Sorcercy, Tunnels & Trolls, GURPS (except for a few sourcebooks), Space Opera, Villains & Vigilantes, Champions, Superworld, Stormbringer, Hawkmoon, Ringworld, Vampire, Mage, Werewolf, Traveller 2300, Twilight 2000, Star Fleet Battles (yeah, not an RPG), Battletech (yeah, not an RPG), Mechwarrior, Car Wars (yeah, yeah), James Bond 007, and probably a few more I don't remember off the top of my head.
No regrets, so far.