Watch this elegant desktop Stirling engine go over 2000 RPM

boing
12

Lee Valley sells a low-temperature one that can be powered by the heat from a coffee cup or even sunshine.

http://www.leevalley.com/en/gifts/page.aspx?p=66742&cat=4,53210,66742

It looks to be the same as the low-temp ones in the link you posted.