Check out the Akai line up. I ended up getting an MPK49 (full on 49 key keyboard controller with the MPC drum pads) and it works killer off my Macbook Pro - totally through USB, no latency or the like, perfect. ANYWAY - in my research of finding an appropriate MIDI keyboard controller, I came to realize there's a lot of respect for the Akai product in the sense of drum pads, beat pads, and controllers. FWIW, I run my SD2.0 through Reaper and the MPK49. It's still a fairly new acquisition, so I can't say I'm experienced at it at all quite yet - but I've found it to be intuitive, and thus far, very responsive and solid feeling. I'd imagine their drum-software specific controllers are the same, and they are renowned for their MPC systems.
Hope this helps.
Mo