How about this h-bridge, 50V, 20A
http://www.irf.com/product-info/data...rel/m3h310.pdf
I got my picstep working yesterday, drove the keling 282 oz-in steppers without warming up much using a 40V supply, no mechanical load though. Used some old pentium 2 cpu heatsinks I had, didnt need to hook up the fans on them. This was the first time I built anything with a PIC in it, they are impressive little devices.