I have been working on a few different designs for a holonomic drive robot. A true platform like the other killough platforms made from Lego would probably contain wheels that rotate differently, but I wanted to publish this design because it is interesting.
I tried two different versions that you can see in the movie below. One version uses wheels but I also built this platform into a three legged walker.
The walker configuration is shown in the pictures, the video shows both versions.
I also set up a simple collision detection loop for this robot using the ultrasonic sensor.
Head on shot:
The undercarriage is a fairly sturdy triangle.
Bigger pictures can be found in my Lego Mindstorms NXT Picture gallery.