[RyanN]

We've used a fiberglass / balsa wood composite board that is very light, but very strong. It drills easily as well. We use a bolt-through design though.

Don't use plexiglass or acrylic. They crack and snap easily. Lexan is the way to go if you want to use something like it.

Plywood works great as well, just a little heavier than all the others. I know of some teams that also use peg-board, which you can get at Lowes or Home Depot.