I like Ableton Live, it's a neat program.
LiveAPI
LiveAPI was my project to get access to the embedded Python interpreter that runs LiveAPI's interface. With the help of Rob King and James Andrew we were successful!
There's been an off-shoot project headed up by MDK that seems to be doing pretty good. You can read about it here, their project is seeing much more active development than 'classic' LiveAPI.
LiveAPI was featured in MusicTech magazine which was pretty neat.
Here's a nice video of LiveAPI being used in conjunction with a Jazz Mutant Lemur