OK, here are my eight OTOH, in no particular order. i don't care how feasable they would be, because you told me i'm in charge.
Nostalgia Monster Book: Yeah, this one is pure fan-service. Granted, yeah, we have the Tome of Horrors, but I think a lot of people want to see a full color book from WotC. I know I'm not the only one who's sad to see MMIII move farther from the idea of using monster conversions, and MMIV and MMV totally abandon the concept - the well is not as dry as some people would have you believe. What I'm saying is, let's see a monster book updating the best ideas from the 1E hardcovers, the Monstrous Compendium series, Dragon and Dungeon, old modules, etc. Come on, of the thousands of unconverted monsters (just ask Echohawk - he counted them all!), there have to be at least a few dozen that are worth revisiting!
Even if that's a challenge, just cull some from the hardcovers and Paizo mags of the last few years to supplement what's converted from the older materials.
Fiendish Codex III: Let's get the yugoloths, and put Todd Stewart in charge of it.
There's a lot going on with these guys than what the 3E designers have bothered to reveal! The baernaloths have their hands in everything, and the mighty altraloths have plans that affect everything from the other fiends to the celestials and beyond. Of course, maybe the yugos just don't want their secrets revealed...
Fey Book: Similar in focus to Libris Mortis, Lords of Madness, Draconomicon, and the Fiendish Codices, let's get a book about fey going. We can show the light, whimsical side, as well as the dark and sinister side of the Queen of Air and Darnkess and her kin. Let's give DMs who would never consider using fey as an encounter a reason to change their minds. We would include monster conversions of Leprechauns, Quicklings, and a bunch of other old and new fey.
Elemental Planes book: This book would follow in the same grain, except focusing on elementals and creatures of the elemental planes. I'm pretty much just echoing Shade on this one.
Spawn of Chaos: This would be Limbo's answer to the Fiendish Codexes.
Let's get some details going about the slaadi and what makes them tick, as well as reintroducing the powerful slaad lords: there are of course the famous Ygorl and Ssendam, whose names have been bandied about since nearly the beginning of 3E but never really detailed, and the less well known Rennbuu and Chourst from Dragon #221, and hell why couldn't there be a dozen more.
The slaadi may not fill a whole book, but of course Limbo is also home to the githzerai, so they would get a full treatment as well.
Legions of the Holy: There may not be a demand to have an FC-style book for each of the angels, archons, eladrins, and guardinals, but why not do a single book for all of them? This book would have a similar detail level to the FC's, but would focus more on how celestials help other creatures (and what they can do when you get on their bad side).
Monster Mythology: This book would be something like an update of the old 2E book about monster gods, and would be in the vein of the "Complete Devine" section about gods. The difference is, I would cut out the PC races gods (and dragons, they got the Draconomicon) and any demon lords, and focus on the drow, orc, etc monster pantheons and assorted miscellaneous gods of non-humanoids which haven't gotten much attention elsewhere in 3E. You could toss in the gods from books like Libris Mortis and Lords of Madness, plus other interesting things like the neogi gods from Dragon #214, and the elemental gods (Kossuth, Istishia, Grumbar, Akadi).
Book of Artifacts: This book would be another update of a 2E book. This would collect a number of artifacts from the DMG and other books, and really expand on what they are and what they can do. It would also feature a system for creating new artifacts and governing how their powers work. Variant rules could include making artifacts work similarly to Legacy items, or the "random power" idea from the 1E DMG, or the system used in the 2E BoA, or all of the above.
I would be more than happy to work on any or all of these books, even if I don't have the time for it.
