So without further ado:
Confirmed lesser gods (source in parentheses):
- Tiamat (Draconomicon I) - merely half of the original god Io.
- Bahamut (Draconomicon II) - Same deal as Tiamat
- Vecna (Open Grave) - Possibly the youngest god, started out as a mortal and progressed through lichhood into godhood.
- Torog (Underdark) - Beaten up and imprisoned in the Underdark, away from the Astral Sea. You figure that does a number on a god?
- Lolth (Monster Manual III) - Cast down into the Abyss, acting as a demon queen rather than a goddess.
Confirmed greater god:
- Bane. He got an article in Dragon #372, statting his aspects, and in the aftermath the writer spoke up, mentioning that Bane was officially to high level to stat up.
- Asmodeus, Avandra, Corellon, Erathis, Gruumsh, Ioun, Kord, Melora, Moradin, Pelor, The Raven Queen, Sehanine, Tharizdun and Zehir.
So let's speculate a bit:
- Asmodeus - Newish, like Vecna, and sealed up in Baator. On the other hand, he did take down a god, and probably has great personal power within his prison. In the interest of making a great villain available as a campaign capstone, I'd err towards Lesser God.
- Gruumsh is locked in battle with Bane and that guy hasn't walked over and killed him yet. It could be because even gods balk at wading through entire armies, but I'd still peg the guy at Greater God. Going back alphabethically, that implies that...
- Corellon would be a Greater God, since he beat Gruumsh in a duel.
- Tharizdun - yeah, I'm skipping a lot of good gods here, going straight for the one that's been locked up in the Cosmic Loony Bin for aeons. Taking him down in the first place took most of the other gods, but maybe he's been weakened during his imprisonment. For the same reasons as with Asmodeus, I'd tag him as a Lesser God.
- Zehir, finally, is a tricky one. He's waging a constant war with Tiamat (though not quite as violent as the one between Gruumsh and Bane) who is already pegged as Lesser. One could assume he's a terrible foe if he's prepared, but if you corner him without his strongest poisons available, he's a Lesser God. The Batman of the Gods, so to speak.