Brick Labs

Mindstorm Manifest has some building instructions for some custom models.  Most of them are based on the RCX, but there are some that are strictly Technic.

One of my favorites is the Mclaren F1 car.  Built to scale with a working gearbox, suspension, doors and a V12 engine!

There are some neat sub-models too.  Like the Splitter (converts a single motor output to a left-turning and right-turning output), and a steerable walking robot (called the  Hexapod). He also has a Battlebot, made from the RCX system.  It actually uses two RCX’s, one for the joystick, and one for the bot itself.

Alas, the site seems to be dormant.  Nothing updated in awhile.  But there are still some great models here.