For one, I want to emphasize/clarify that IMC, there will be core classes available to the PCs, and core classes that will be NPC-only.
For PCs, there's all 11 of the PHB core classes, all 4 of the XPH classes, CW's samurai & swashbuckler, CD's shugenja, & CAr's wu jen. (I'll probably at least allow scout & ninja from Complete Adventurer; I'll have to review the spellfilcher before I consider it). I'll also allow the CG "paladin of freedom" variant from UA, though they're core class name is "Avenger."
For NPCs, there's all of the PC-allowed classes, plus the NPC classes from the DMG (which makes up most of the NPCs/population), CW's hexblade, & CAr's warlock. There's also the LE "paladin of tyranny" (or "Blackguard") & the CE "paladin of slaughter" (or "Ravager") from UA as well.
I don't like anything reminiscent of MAD, so that's why I didn't allow CD's spirirt shaman or favored soul. PCs can sorta-kinda replicate the basic concept of a warmage through a multiclassed sorcerer.
I was considering using the classes from OA, but some of the mechanics in there didn't seem that easy to mesh with standard D&D (which is what I was going fro, rather than running a pure OA-based/themed game).