What's your setup?
Almost any midi keyboard can shoot a few midi notes into a sequencer but the question is if you need any other midi data to be be sent from the controller.  If not then you can hit the pawn shop and grab a old casio with midi out for the $30 to tap notes. But  you may want some sliders on that piece to give you some hands on faders for your daw or something. Also... What's your skill level on the keys? Even if it's pitiful you may plan to learn to play a full 88 keys one day. 61 and 49 has been cool with me for tapping out beats though. You may have space issues... Maybe you should think about killing 2 birds with one shot i you need more sounds. Do you need some more sounds to boot?  Last but most inportant...  What are you spending? 
Fools around here got enough junk to help you make a good choice so figure what you need and somebody should point you in the right direction. Wish I knew about this spot when I was spending. 
Think about it some and hit back..