Moe Tousignant pointed out on G+ that there appear to be plans afoot to republish the 2e PHB. 2e doesn't get a lot of love on the intrawebs, but it's probably the system I had the most fun with. (Ok, that's not entirely true. My college games, and those that grew out of them, were driven by 2e PHBs and 1e's DMG, Manual of the Planes, a handful of D&D books, and, in later years, the Book of Vile Darkness. But you get my point.)
2e got a lot wrong, including decoupling EXP from gp and a lot that can be traced to the ideas that resulted in James Ward's "Angry Mother Syndrome" editorial in DRAGON #154. 2e also got a lot right, however. Among them were specialty priests and arranging clerical spells into spheres of influence (and, in general, I love what 2e did with clerics) and awesome settings like Dark Sun, Birthright, and Planescape.
The best thing to come out of 2e, in my estimation, was the Monstrous Manual. Ok, yes, the whole demons/devils/baatezu/whatever nonsense was lame, and some of the art was mediocre. However, it had some of the best write-ups for monsters ever. It's the one that gave us all the great "and the gizzard can be used in potions of pudding-breathing" type details that eventually inspired Noisms' excellent "Let's Read the 2nd Edition Monsterous Manual" thread on RPG.net, one of the most epic threads ever to grace that site. The result was an amazing collection of campaign and adventure ideas for every single critter in the book! (The link goes to his pdf collection of the ideas, not the thread at RPG.net.)
Luckily, it appears that the Monstrous Manual is also slated for re-release. If you play any old-school game I heartily recommend you pick it up; other than possibly translating AC from descending to ascending, the only other thing you'd need to worry about is a mild case of hit point inflation. And even if you don't use the stats, as Noisms showed, there's a wealth of inspirational material in that book.
If you haven't yet, I'd also heartily recommend picking up a copy of the 1e DMG. Yes, it's chock-full of Gygaxianisms; yes, its poorly organized. But it's also the best resource for running a fantasy RPG of any edition or rules I've ever read. From lists of the magical properties of gems or the healing properties of herbs, to random tables for generating and stocking dungeons, to explanations of government types and noble titles, the book is just bursting with useful stuff I want when I'm designing campaigns, creating adventures, and running sessions. But, as they used to say on Reading Rainbow, don't take my word for it.