Propellerhead's new Reason 3.0 is looking very interesting. They've developed several new features designed for live use, including the Combinator which allows you to store complex combinations of virtual devices/samples/patches/effects as a single patch that can be recalled as a midi program. New sample browser too. I've always been interested in using Reason live but it didn't seem practical until now. You could get a laptop and Reason for almost what the Motif Rack ES will sell for and have a lot more bang for the buck, not to mention a whole fleet of new sounds. Check out Reason here:
http://www.propellerheads.se/