I stumbled on this while looking for some casters. I haven't tried it yet, but they look really nice: http://www.castercity.com/workbench/easy-workbench.htm
I don't like how the legs get attached to the bottom cross-braces where the wheels are mounted. A mortise and tenon or exterior plates would greatly increase the strength.
they have lag bolts going into the end-grain of fir, If you have a bit of a load on there, push too quickly and the wheels hit something you could end up with a toppling workbench.
