I'm running a 3.5 game and playing in another one. Each game meets 2x a month, for about 5 or 6 hours each session. So generally, I'm either playing or DMing a game once each week.
The game in which I am a player is populated by mostly neutral characters who are quite willing to blow off any hero work, abandon towns to their fate, and head off treasure hunting. In this game, it
appears that any official WotC 3.5 edition product is allowed. I italicize "appears" because there is no official list of allowed books. But anything I've wanted from the Complete series or other books (such as the SpC or PHB2) has been OK.
For the game in which I am the DM, I allow the following books:
- Player's Handbook
- Dungeon Master's Guide
- Monster Manual
- Dungeon Master's Guide 2
- Player's Handbook 2, but no "rebuilding" rules and the "retraining" rules are limited
- Complete Divine
- Complete Arcane
- Complete Mage, but the feats Precocious Apprentice & Collegiate Wizard have been nerfed
- Complete Adventurer
- Complete Warrior
- part of Complete Scoundrel (chapter 5, the loot; and combat trapsmith class)
- part of Complete Champion (chapter 3, the spells; and chapter 4, the loot)
- Magic Item Compendium
- Spell Compendium
- Forgotten Realms Campaign Setting book -- only pages 95-97, in particular the bandoleer, potion belt, scroll organizer. I have house-ruled that these items enable someone to use the Quick Draw feat to quick draw things that might normally not qualify for Quick Draw (such as "non-weaponlike items" such as scrolls).
- En World "Critters" series -- PDFs that have fan-made monsters
- Tome of Horrors 3.5 revision, from Necromancer Press, I think
- Toolbox book from AEG
- About 40 pre-approved feats from the Net Book of Feats (I copied the text for each feat I approved and put it into a private forum for my players to review)
- Ultimate NPCs, from Mongoose Press
- Denizens of Avadnu, a monster book from Inner Circle
- Blackdirge's Dungeon Denizens, a monster book from Goodman Games
- Creatures of Freeport, a monster book from Green Ronin
- Necromantic Lore, a monster book from Fantasy Flight Games
- Creature Collection revised, a monster book from Sword & Sorcery (catching a theme here???)
- 40 Alchemical Items, from Adamant Entertainment
- The Lazy GM - Goblinoids, from Creative Conclave
- Three Dragon Ante, for whenever the characters try to gamble
- Book of Taverns, from Sword & Sorcery*
- Grim Tales Mass Combat, a 16 page PDF subset of the bigger book, Slavelords of Cydonia, by Bad Axe Games - I don't think this is available any more.
Whew! I think that's actually precisely everything I use, no more no less. The ones
highlighted with color are the ones that I use the most. Also, I used to be a big advocate of The Noble Wild, a great PDF that enables Narnia-like talking animals in your D&D campaign. However, I grew weary of the extra rules and eventually just said, "some animals can talk, they use the same mechanics as others who can speak." Nonetheless, if you want a really cool system for animals -- including lots of animal-specific spells & feats -- then it's a good book for you.
Oh, I could also walk you through all the modules that I use, but basically it's just all the Dungeon Crawl Classics from Goodman Games (including the two hard-bound compilations) and all the free modules online at wizards.com.
* Unlike all the other books, which are generally useful to many DMs, I can't recommend this book in general. I love it, but it is specifically only for DMs who care so much about taverns & inns that they crave backstories and pre-generated barkeeps & barmaids, and so on. My players loved The Witch's Teat tavern, and spent many hours fighting in the tavern "pit."