See: http://lua.org/
Lua is a bit like Javascript, a bit like Python, a bit like Ruby...
It's small, fast, and written purely in C. It can be VERY easily embedded into any application, or run standalone through the Lua interpreter.
If you haven't tried it, do so!
Discussion (3)
As a general-purpose language, give me Perl any day. However, Lua's supreme focus on ease of embedding (and minimal dependencies) means that it's starting to replace crufty, home-grown scripting languages with something sanitary, sane, and capable of closures.
I look forward to the day -- no doubt far distant into the future -- where Lua becomes the standard scripting language in a popular IRC client. (I'm looking at you, mIRC! And don't think I've forgotten about you, KVirc!)
It's good. But guile is soooo cool and very easy to embed.
Io is another prototype-based language with a goal of embedded scripting. Not a very pretty core lib yet, but extremely reflective, practically as much as Scheme et al. (hard to compare because it is so consistently OO).