Since my mom threw out my Basic D&D set, I was left with only my even more treasured Star Frontiers: Alpha Dawn (the original rules for planetside adventures) and Star Frontiers: Knight Hawks (the later released rules for adventures in space) boxed sets, as well as the first and only Zebulon's Guide with the revamped rules set for the longest time. Later on I discovered Gamma World (4th Edition) and fell in love with the random mutations that could be either beneficial or highly amusing defects. I've still got all of those, including all the half-inch squared counters for the Star Frontiers games.
Throughout the years I've also owned, Dark Conspiracy, Shadowrun, Renegade Legion, and a few other PnP RPG's. Most of these others though I've since traded away. Most recently purchased of my PnP collection includes the D&D 3rd Edition core rulebooks including the Player's Handbook, Dungeon Master's Guide, and both Monster Manuals.
*big sighs of nostalgia*