If you are looking for an extra sound source and a basic MIDI controller on the cheap, look no further. Casio's CTK-451 ($159.99) is five-part multitimbral, displays music notation on its screen, and responds to Velocity messages over MIDI. It has built-in speakers and runs on AC or batteries, so you can take it anywhere. All you need is a couple of MIDI cables and a laptop computer for composing when inspiration strikes.