If you have the money and the desire, I highly recommend keyboard + midi interface + mixing software. It'll cost quite a bit to get a setup that isn't crappy, though - $200-300+ for a decent keyboard, about $30 for a 1-1 midi interface, and an insane amount of money for the software and samples, which really depends on how obsessed you are. I've spent about $400 on my whole setup so far.