If you really want to get a keyboard controller, Yamaha has a new line of controllers (no sounds on board) that are not too expensive.

There are about 5 models including:
KX49 - 49 keys
KX61 - 61 keys
KX8 - 88 weighted piano style keys.

I have a lot of Yamaha gear and have never been disappointed in the quality. M-Audio also makes some inexpensive controllers, but I can't vouch for the quality.