The "gems" of my collection (in no particular order):
First Fantasy Campaign (Judges' Guild)
The entire line of Star Frontiers boxed sets, modules, and supplements (yup, if it was printed for Star Frontiers, I have it - I don't have all the minis, though, and am not interested in collecting them).
Grimtooth's Traps, Traps Too, Traps Fore, Traps Ate, Traps Lite, and Grimtooth's Dungeon of Doom (Flying Buffalo)
1e PHB, DMG, MM, FF, MMII, UA, and D&Dg (all in excellent condition, I might add)
The Rules Cyclopedia and AC 9, the Creature Catalog
I don't yet treasure my 3e stuff in quite the way I love some of these old things (nostalgia, I guess, but also the fact that many of them would be quite hard to replace), but I'm sure with time, I'll get there.
--The Sigil