if you decide to go for knobs, I suggest the EMU XBoard 61 . for a few bucks more you get better keyboard (still plastic, but...) and
aftertouch . more knobs, too if aftertouch is not a plus for you (but it should be) and the X-Board is out of budget, the M-Audio Oxygen costs the same as the KeyStation. and still better than the Behringer. another suggestion: go in a shop and...