Try Litko's BaseMaker™ tool. Choose to have your base made from any of 20 different materials. You can even get special features like rounded corners on your bases.
These bases measure at a precise 40mm x 20mm. I am mounting all of my new miniatures on Litko plywood bases. These bases lay perfectly flat, and do not have to be straitened out as metal bases some times require. The edges are smooth out of the bag; I occasionally needed to file smooth the edges on metal bases. Another big plus is that I can use common white glue to mount the miniatures. A great product.