The story has been told many a time. There once was a great avant-garde rock group who got picked up by Andy Warhol, enjoyed (very) moderate record sales of their four albums - Cale got ousted by Reed after the second one - and today is an inspiration for anyone with a craving for dissonants, drones and depravity. And oh, there was a reunion tour in 1993.
This site does not cover that story. You need only visit one site to learn everything you always wanted know:
The Velvet Underground Web Page
Subtitled Electricity comes from other planets, it covers the whole story. Includes an up-to-date news section. Maintained by Olivier Landemaine.
Still here? Let's see.