What are the MOST USED pre-3e D&D/AD&D books.

[Davelozzi]

Currently, I'm making good use of much of my Dark Sun collection, especially the original campaign set.

More generally:

The DM's screen from the Birthright boxed set. I've never run a Birthright campaign but the art side is more to my liking than any other screen I own. I generally keep it out facing the players and layer a 3e DM's screen on the inside for the actual info.

World Builder's Guidebook - This excellent book saw extensive use when I was first drawing up my homebrew.

Player's Handbook - I still refer to this quite a bit for the carrying capacities of various containers (backpacks, sacks, chests, etc). I wish they'd included that in the 3e (and 3.5) versions.

And as Eric said, Faiths & Avatars and it's successors Powers & Pantheons and Demihuman Deities are generally pretty useful. I haven't ran a 3e FR campaign but I'd probably use them quite a bit if I did. But even so, I've still refered to them a number of times just to check something or get ideas for naming a knighly order, mapping a temple, or whatever.

Finally, it's not uncommon for me to occasionally refer to any of the old monster books, especially the first Planescape Monstrous Compendium. I love having all of the important fiends gathered in one place, and also enjoy DiTerlizzi's illustrations of them.

 

[MarauderX]

I still use the various Basic D&D Gazeteers a lot, for maps. The maps in Greenwood's Halflings book (Basically the best of the entire lot; here we get a real name for the halfling race, as well as what I think are the very first depictions of halflings as something other than disgusting little butterballs.

The city maps from various modules (before the 'FR Style' ruined that source), particularly the UK-produced modules (which always had, hands down, the best maps in any TSR project until unless it was Dragonlance or the original Ravenloft module). Night's Dark Terror maps still see a lot of use, as do the maps from various OA modules.

I agree with the OD&D gazeteers, only for the cultural setting goodness, and leave the maps behind.
Plus any adventures from OD&D are usually awesome, even the companions and masters series where things started to get out of hand (Earthshaker anyone?).

 

[Arnwyn]

I still use a lot of 1e and 2e books:

- all the FR accessories
- loads of 1e and 2e modules
- Of Ships & the Sea
- Al-Qadim (everything)
- Planescape (everything)
- Spelljammer (most of it)
- Monstrous Compendiums (I've updated everything that wasn't to 3.5)

 

[DaveMage]

Faiths & Avatars
Tome of Magic
Encyclopedia Magica
Planescape Monster Books

 

[Phaedrus]

World Builders Guidebook. I really like that one!

 

[vortex]

I used Unearthed Arcana so much, I wore out the binding

 

[Davelozzi]

I used Unearthed Arcana so much, I wore out the binding

I used it once, maybe twice, and I wore out the binding too. I credit it to the crappy manufacturing, not to the game design.