We spend a lot of time designing and perfecting our omni-wheels.
We started using Knex wheels as the rollers:
http://www.chiefdelphi.com/media/photos/16984
Those were replaced with plastic rollers:
http://www.chiefdelphi.com/media/photos/17047
The two layers of carbon fiber (legalized in 2004) were eventually replaced with a single sheet of aluminum and plastic rollers replaced with rubber...and then we switched to AndyMark.
We used the Bosch drill transmissions in 2003 and 2004, Nothing But Dewalts (3 speeds!) from 2005 to 2007. I can remember rebuilding the Bosch transmissions every 2-3 matches at IRI in 2003. We had a horrible time with those.
Our frames were 80/20 for our first two years, a modified IFI kit frame in 2005, and in 2006 we designed our first sheet metal chassis.
Mike Trapp of Waterjet Cutting of Indiana began helping us in 2004 so we had the advantage of getting custom aluminum sprockets and gears cut for us.