MLCad
Windows based Lego CAD program. Very cool software for building all kinds of models, and the great thing is you don't have to worry about running out of parts or colors.

Master Grade Legos
This site is too awesome for words. I'm not worthy.…

Marsbase
A very impressive Lego mech site. ****

LeoCAD
Windows based Lego CAD program. One of the cool features of this program is the Minifig Generator.

Lego Corporation
The creator of all those amazing building bricks we have come to love so much. ^_^

LDraw.org
The place for all things related to modeling and rendering Lego models.

Dat2DXF Converter
Very useful tool for converting .dat file to DXF format files. The DXF can be imported into just about 3D rendering software. One of my can'nt live without Lego files.