You could use a bass amp. But unless your keys are strictly for bass related material, you'll want either a dedicated keyboard amp or PA. They'll offer much better full range capibilities. Check the Roland KC or Peavey KB/A lines both are decent and come in a variety of sizes depending on your needs. One thing to consider is that with a dedicated PA you can retain stereo Imaging (Or 2 dedicated keyboard amps will). But if you need a little more thunder-down-under, then by all means grab a bass amp, but you should be able to at least find a deidicated amp to meet your needs within the same price range as bass-amp. And if you get a 15" model you'll be able to reproduce frequencies almost as low as bass amp (anything lower than what these amps can produce usually warrants the purchase of sub add-on anyways.)