I use Extempore by Andrew Sorensen, which grew out of his Impromptu work [1]. It is a livecoding environment with its own language xtlang (vs. Clojure on the VM for Overtone). Watch some of his videos linked on the site, or on YouTube. Pretty incredible.

Lately, I realized I am not much of a livecoder in the same respect that I am not a performing musician. I have now picked up Euterpea again, a Haskell-based livecoding environment that you can compose at the signal or note level, but it is not really suited for live performance [2].

Grace, an all-in-one download, multi-platform, scheme-based music coding environment based upon Common Music (CM) is a great way to start without having to do much setup. It has great tutorials and samples in the menu under Help [3].

Livecoding is definitely more popular overseas than in the U.S. although there was recently an algorave in NY this year.

[1] http://extempore.moso.com.au/ [2] http://haskell.cs.yale.edu/euterpea/ [3] http://commonmusic.sourceforge.net