BlockCAD
3D fun drawing program uses Lego like blocks. Provides a gallery, downloads, and instructions.
Ldraw.org
A freeware program which can create Lego models in 3D. Learn about LDraw and download related software.
LEGO CAD: Simple Machines
A computer-based educational LEGO building kit, designed to teach concepts in basic machines.
LeoCAD
A CAD program that uses bricks similar to those found in many toys. The program can import LDraw files.
Paul Gyugyi's LDLITE Version 2.0
A program that displays 3D Lego models. Platform, release dates, and installation information provided.
The LDraw model repository
Building instructions for official models (in LDraw format).