A reader pointed me to the Fujitsu 6140. It is faster than the Scan Snap at 80 to 120 ppm (each side counts as one page) and seems to be a little more heavy duty in its construction.
It looks like it uses dual rollers where the Scan Snap 510 and 510M only use one. This might help guard against misfeeds and paper jams.
The 6140 comes with Kofax workgroup software that will handle some scanning tasks including processing bar codes scanned on documents. The scanner appears to only support the Windows platform.
The 6140 is quite a bit more expensive with a list price of $1999. You can get it in the Productivity501 Store for $1,660.