M-Audio Keystation e49
I had one of those and took it back within a week, it had stuck notes!
Ross C, download the fruityloops demo, and see how low you can get the latency with a few heavy CPU synths loaded. Fruityloops uses ASIO and even comes with ASIO4ALL which is really quite handy.
Thats the best way to see how your system will fare since price doesnt necesarily equal latency.