Chez Scheme (the compiled version vs. Petite Chez) figures high on those lists, and it was just opensourced by Cisco. I used to use Gambit-C, and I still like it, but Chez is fast.
I am playing with Eduardo Cavazos's libraries with Chez [1], and particularly the port of xspringies. Great fun considering as he points out that the mass-spring calcs are all taking place in scheme. It runs fine on my 2-3 year old notebook.
C was a third language for me in the day, and I like Lisps, so this Lispy-C thing is going to eat my afternoon up!
