Most drow cities occupy large vaults/caverns in the Middledark. At these depths, faerzress is common and powerful. The drow have developed many potent spells and defenses that harness the Underdark's magical radiation for their own purposes. The Middledark also offers the defense of distance--a drow outpost near the surface is vulnerable to the attacks of adventurers and surface elves, but moving a large army into the Middledark can't be done with ease.Taken as a whole, drow probably have the most significant presence in the Middledark. Their cities and strongholds are numerous, wealthy, and well suited for defense, and the drow themselves are cruel and strong. Only the endles feuding of the great Houses constrains drow power. Menzoberranzan is the most famous of drow cities.
Sites of information
http://drowcampaign.roleplaynexus.com/underdarkdenizens.html
http://en.wikipedia.org/wiki/Drow_(Dungeons_&_Dragons)
http://en.wikipedia.org/wiki/Drow_deities

Information forthcoming.