Well since you asked.... :)
I'd be more than happy to plop down my hard earned cash for supplements dealing with the various races and settings. As for as the races thing, I would specifically suggestions for variations on the races (tinker type gnomes vs the more traditional gnomes, for instance). I'd also like to see a treatment of undead as a race (like the Forsaken in WoW).
Prestige classes... my opinion on these are that they should be mostly just for flavor and shouldn't go past fifth level. I like what the FR base setting book did with these. I don't think there's a lot of need to beat the classes to death, but I do think that the cavalier and the swashbuckler just never got enough love in 3.5 (or 4 for that matter).
I would also spend my hard earned money on bestiaries, but that comes way after the aforementioned things.