Forgotten Realms Drow pantheon: [ Lolth | Vhaeraun | Eilistraee | Ghaunadaur ]
Lolth is probably the goddess that most people immediately associate with the Drow. Yes, Lolth is the goddess that most drow worship, and who fuels their evil nature in many ways.
The Spider Queen, the Queen of the Demonweb Pits... Lolth.
Lolth is, technically speaking, an interloper deity, which is a fancy way of saying that she exists in multiple worlds - there may be subtle differences, but she is essentially the same goddess in all of the worlds. The following - and her connection with other drow deities in above list - is from Faerûn (Forgotten Realms).
Lolth was once Araushnee, the consort of Corellon Larethian - the great god revered by the elvenkind, and bore him twins, Vhaeraun and Eilistraee. She was the patron of artisans. But then, she turned against her lover: She helped Gruumsh and Malar to fight against Corellon, and as that was fruitless, finally assaulted the realm of Arvandor with the aid of hostile spirits. But, of course, that failed, because Corellon Larethian isn't that easy to beat. For her treachery, Araushnee was banished into the Abyss, with her form turned into that of hideous spider demon. Thus, Araushnee became Lolth. Lolth gained power on the Abyss, and with help of Vhaeraun and Ghaunadaur, she cultivated and captured to her the warlike elven folk of Illythiiri - who were cursed by the elven pantheon and banished to the Underdark for following such evil deities. Thus the Illythiiri became Drow.
Now, Lolth is a tricky goddess. She is most obviously quite insane, because her normal pastime is trying to make people - her own worshippers - to kill each other in various fun ways. The lives of drow societies are thus filled with internal strife of all kind. Lolth lives of chaos and misery of others, and covets the power of other deities. Worshippers of Lolth are typically required blind obedience and acceptance of the fact that women just simply are the rulers of the world, and men who don't show any talent are better suited for sacrifices. Everything is built on fear and power, and under that layer lies nothing but distrust and chaos. And as for other races... well, if it's any good, just slap 'em on the altar, if not, just kill them on the spot. Oh, and do not hurt the spiders or you - shall - suffer. Spiders good.
Lolth is a Chaotic Evil goddess of Intermediate power, allied with Malar and Loviatar, and is against almost everybody else, the elven pantheon in particular - and Ghaunadaur and Eilistraee, too. She appears, if she needs to appear, either in form of a gigantic spider with a beautiful drow woman's head (or a drider with a beautiful drow woman as the other half), or just as a drow woman. Her symbol is a black spider with a female drow head hanging from a spider web. Her home plane and domain is in the Demonweb Pits.
Lolth's name is also spelled "Lloth" by the drow themselves. (Sabby tells me this was Gary Gygax' own spelling from Greyhawk world, and it was changed to more easily pronounceable form for Forgotten Realms, and is probably going to stay that way. The explanation of how the Drow call her Lloth and the rest of the world call her Lolth was from R.A. Salvatore's book "Exile", I think. The deity fills same role in both Greyhawk and Forgotten Realms.)
(By the way, most of the fundamental 3rd edition books don't give deities armor class, HP, and - oh my goodness - XP value. Shoo! We're trying to scare away the munchkins! Don't fool around! This is a serious RPG! For the utterly epic people, the stats can be found from Faiths and Pantheons book, though.)