A Mighty Fortress - paralleled with my homebrew setting, was used more often in 3.X than 2e.
The Auld Grump
Most good campaign setting books should be. Not that all campaign setting books are good, but still...I'll give an example of a book I think fits this bill, the Neverwinter Campaign Setting. Its choc full of inspiring ideas.
Although I'm not especially a fan of the old Wilderness Survival Guide, I certainly agree tha tthe 3.5 environment focus groups were dreadfully disappointing. Rather than inspire with new ideas, they seemed focused on trying to avoid the very notion of new ideas. Most of what was included was either too silly to be taken seriously, too banal to be interesting, or too obvious to have merited being put into print. And I still laugh at the constant implicit and explicit references to the idea of not actually getting out in the wilderness, but rather just making a room in a dungeon be really cold (or hot, or wet, or whatever, depending on which environment book it was) instead.Wilderness Survival Guide - I wish that the 3.5 terrain books had been half as useful.

Wilderness Survival Guide - I wish that the 3.5 terrain books had been half as useful.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.