Hrm..
I quite like all three of the books that were initially mentioned. I haven't used Lords of Madness, but it looks like fun. MMIII I've used a bit IMCs, and despite its bad press, lacklustre quality and other real flaws, it's not that terrible really. Advanced Bestiary has not been used in the very short time I've had it so far, but there is certainly some great stuff in there, which I'm sure will see use in the near future. . . besides, you can't (often) go wrong with GR, IMO.
It might not be to every GM's tastes, but I've found Denizens of Avadnu (as well as several other books that've been mentioned in this thread) to be worth the price.
I gotta say, it sure is a mismatched selection to be choosing from (MMIII, AB & LoM). Didn't you also mention environmental books? Well, if so, I can honestly say that Frostburn has been very useful to me, in actual play. Stormwrack looks promising, and is somethiing I will no doubt end up purchasing when I get around to it. But you seriously don't need any of them unless you're planning on running those specific kinds of campaigns / sessions.