For NES I used to throw away all my boxes and lost most the books, but i did manage to keep Zelda 2, Final Fantasy, and Metroid in their boxes with the books/maps. Starting with Super Nintendo I started keeping everything in perfect condition with all the books and maps and stuff. I think my most Valuable SNES game (I think its my rarest game of all) is Castlevania Dracula X, which I had no idea was worth anything until recently, I also have Chrono Trigger, Final Fantasy III, and Super Mario rpg all of which I think are somewhat valuable. For N64 my most valuable game is Majoras Mask collectors edition. For Gamecube my most valuable games are Resident Evil Code Veronica X, Pikmin2 and Skies of Arcadia I think are the most valuable ones I have. I also have the gamecube Component video cables which seem to be worth more than any of my games for some reason.