Heroes of Intrigue: A book for running political games and determining the CR of Charisma based challenges (My own personal opinion would be to use the targets Cha Mod).
Complete Epic: Updated epic material.
Feat Compendium: Alot of feats.
Arcadia: A monster book for Fey.
Faiths and Pantheons II: Detailing the defenses of Faerunian temples and what services they offer. Not specific temples but a blanket template based on the type of city they are in and what alignment and what domains the god of the temple has. This way I can rightly say how many Cure Light Wounds potions a temple Chauntea has in Suzail, and what the highest level Cleric is. I know the DMG has stuff to determine NPC's and such but I think we must assume that most NPC Clerics arent very high level since they are tending to the Church. Or perhaps this book could offer faith based challenges that allow the character to gain XP. Also include updates for 3.5 deity's.
Planescape 3.5e: Duh
Spelljammer 3.5e: Duh
More Faerun Regional Books: Finish these off please!!!!!!!
Realms of Toril: Details the regions outiside Faerun, such as Zakahara, Maztica and kara-tar.
Dungeons Masters Guide to Faerun: Basically the DMG but Faerun specific. Such as how common are Thayan Enclaves, and where are they? What does the Black Market sell? What kind of forces do the various nations have. What are the monster frequencies. What are some notable dungeons? Whats the likely hood that a merchant in waterdeep could afford to buy my +5 Vorpal Long Sword (despite the gp limit of a city I find it hard to believe anyone could buy this stuff off of you). What is going to happen in the years to come (Such as the year of Risen Elf kin and Beyond), a DM has to prepare for this kind of thing. Id willingly pay 45 bucks for a good 250-320 pg book on this stuff.
Heroes and Villains of the Realms: Forgotten Realms NPC's fully stated with alternate versions (such as the Dervish Drizzt I see stated occasionally). What they are currently doing and what books they have appeared in. Id say one stat block per page and one description per page. So one npc=2 pages. Preferably they are optimised.
Fiendish Codex III: Yugoloths
Netheril Age: Bring this back! 3.5 true 10th level + spells. Some people want to live in the past.
Monster Compendium: Every monster that has not yet been converted from past editions is in here.
Monsters of Faerun II: A complilation of Faerun monsters that have been scattered about in the books. Plus new ones.
Prestige Class Compendium: Duh
Spell Compendium II: Duh
Arms and Equipment guide II: Same as the first but a better layout, plus new crap too.
Races of War: Details Goblins, Orcs, Gnolls and other waring savage humanoids.
d20 Vehicles: d20 modern book for designing vehicles. I want to know how powerful an tank is compared to a mech! Or if a Air craft carrier could battle a small space ship.
d20 Fantasy: d20 modern set up but D&D type classes set in Earths past. for example a Charismatic hero could take the Sorcery path of talents or the bardic set of Talents or use the ones from d20 mondern.
d20 Horror: Horror in the modern world, with more Cthulhu type themes. and options for slashers and other type of things. Add some Dark Matter material in here. Wishful thinking here but maybe a heroic d20 modern Call of Cthulhu, No sanity, just the Mythos and monsters.
d20 Spectaculars: Bring this out WOTC! You spent money making it now release it!
d20 Atlas: This is basically an Atlas of Earth, But it shows where strange things are going down. Ecompasing everything from Dark Matter to Urban Arcana. The Information is seperated so you can choose what fits in your universe. What the governments know, what secret organizations know and what the religions know. But like I said sperated by campaign theme, with a usuing it all Side Bar or chapter.
d20 Department 7: Everything on this group, whether you play Dark Matter, Urban Arcana or anything else with d20 Modern. Special Classes, Items whatever.
d20 Legends: Book on Urban legend monsters such as the Jersey Devil, and Magical Items like Excalibur and how such items might fit into your d20 modern game.
DMG III: Rules, rules, rules
PHB III: Base classse, skills, feats, equipment, Substitution levels, alternate abilities etc...
Complete Skills: All the skills in one place, with all their uses, and all the new skills too. New tricks.
Unearthed Arcana II: rules to make nay sayers buy your books. Bascially how to make the game simpler, play a classic older edition with the new game, and some newer rules that are easier to add to the current game, maybe so new combat tactics.
Monster Manual VI: New monsters
Animal Compendium: Animals, Animals, Animals! All the animals from past books plus new ones. and none of the made up draconic like ones, Blech! Dinosaurs gotta be in there!
Book of Templates: all the templates in one place, plus new ones.
Ecology of the Monster: Just a book detailing how common monsters really are. How they interact with the ecosystem. They cant be all that common or normal folk and normal animals couldnt survive in an are where lets say ravnous trolls live. This would be more of a blanket book, as a general rule type of thing, not detailing specific monsters but maybe using them in examples.
d20 Halo: Why not? Wishful thinking, I know.