Well, it depends on what sort of music you want to produce, and how you want to produce it. A good keyboard for trace, dance, techno, and sfx, is the quasimidi raven. It's pretty simple to use, you just either create or choose from 400 non-copyrited beats/sounds/whatever, and put them together. It's got a pretty powerfull onboard sequencer, but I've got mine linnked up with cubase and it's GREAT. I even know someone who uses the raven by itself for his whole set!
If you want something more drum&bass/house/etc orientated then there are a number of options. I wouldn't go for a keyboard. I'd probably go for a series of drum machines, sequencers, samplers, and other gizmos. Oh yeah, and if you hook the raven up to a korg prophecy, you get soume of the phatest sounds since hiroshima!