Multiple votes for From Stone to Steel!...whatever happened to those guys...
Fav D20 hardback is D20 CoC, and that is not D&D (though it can be, and others have listed it)...and favourite D&D is not nec. hardback. Grimm Tales is also good, but also not D&D
In the spirit of the pole,
Tome of Horrors
From Stone to Steel
Manual of the Planes
Unearthed Arcana
with AU, Book of Fiends, Draconomicon, ToH II, and Comp. Book of Eld. Might as honorable mentions
One of the reasons I started this thread is to see what other people think is essential and also see if I'm missing any books that might interest me. So far I think I'll stick to my list but I'm a little surprised at some of the books listed and also at some of the ommissions. For example, I'm a bit surprised to see so many people list the Manual of the Planes as one of their top 5. Sure the book is nice but top 5? Same thing goes with the Tome of Horrors and The Book of Vile Darkness.
On the plus side I'm glad to see the Complete Book of Eldritch Might on so many people's list. It's on my list of books to buy and this thread has moved it to the top of the list.
I know tastes vary but I recommend people branch out from the customary and try some of the better 3rd party publishers like Green Ronin. I think some of you will find it worthwhile.
Well, yeah, Manual of the Planes is one of the best "official" D&D books yet published. I still pull it out every so often just to read sections of it when I'm bored.
And I think a lot of Green Ronin mentions were out there; I saw a lot of Book of Fiends and Book of the Righteous mentioend.