I'm a huge fan of Scheme. Not so much because of the language itself as for its ubiquity. You can find a Scheme interpreter for almost any platform, and for those that don't have one yet, it's actually tractable to implement an interpreter yourself (in some other language).

It's also a very elegant and beautiful language. At the end of the day, though, your customers care whether your product is beautiful, less so whether the code is beautiful.

I've never used CL.