So, recently my reading of OSRIC inspired me to get my hands on the old AD&D books. Thanks to one of my favorite websites of all time, Abebooks.com, I was able to procure the PHB, DMG, MM, and OE for about $25, with the vast majority of that cost being shipping from four different vendors. The MM arrived today, with all of its Lurker Above Dick DM Monster Goodness. Hopefully the rest of them will arrive during the week... the missus goes out of town next weekend and I'll have plenty of time to pour through them.
I'm contemplating going after the MMII, Fiend Folio, Wilderness and Dungeon Survival guides... probably not Unearthed Arcana, which I never owned but have yet to hear many good things about.
I would also kind of like to get my hands on the four Hackmaster "class" books, but these are long term goals, as I have no plans to run any old school fantasy in the foreseeable future. (Though I must admit I've got that itch in the back of my mind.) I figure I can collect them slowly over the weeks and months.