PC's Empire

A collection of LEGO mania presented by Preston and Catherine Crow.

I haven't updated this in many years, but that's about to change...

Stuff from 1995 and before:

The official LEGO site.
The New England LEGO Users Group
LEGO Users Group Network
rec.toys.lego
David Karr's page includes a discussion of a number of models, including one from here.
Paul Gyugyi has a page with raytraced CAD images of LEGO designs. It's quite impressive.
Ben and Jer's LEGO Raytracing is incredible.
Jacob Sparre Andersen's LEGO page
Vincent Harris ("Winco") has a LEGO walking robot (With video)