Yes, I do have the Underdark book (and I like it a lot), but it doesn't have a complete adventure, let alone a campaign. It has a very short mini-adventure in the back. I was looking more for an exploration-travelling adventure that takes the party from one end of the Underdark to the other (specifically, from Araumycos to the Vault of Conjured Madness).
Apart from drow, there are many interesting races and locales in the Underdark. It's too bad the dark elves get all the attention. Duergar, svirfneblin, myconid empires, night demons, slyths, the new Deep Imaskari race, grimlocks, kuo-toa, gloamings, all those are really great adventure material. And that's not even including the other famous underdark creatures like aboleths and mind flayers.
I can make my own adventure, of course, but I would have thought that the hordes of d20 publishers would have filled this niche already.