Great discussuion. In the past year I have met two people who work for a company in Pasco, WA that make large electrical generator plants using solar mirrors, high temp helium gas and a stirling engine. Amazing technology.
Not sure if this is the company, but appears to have just filed for bankrupcy.
UPDATE: Stirling Energy Systems' Bankruptcy Latest In Solar Industry Woes - WSJ.com
Here a link for the American Stiriling company, they sell educational kits.
Stirling Engine or Sterling Engine by American Stirling Company
And one for the Quaisturbine Stiling engine
Quasiturbine Stirling Engine (Sterling) - Rotary Hot Air Motor - Heat Pump
I thought at least one car manufacture already made a stirling engine car, but google shows nothing.