You might want to consider an Akai MPD-16. Although it's not a drum machine, it's the pads from an MPC with no brains behind them.

The reason why I bring it up is that once you assign drums, loop fragments and FX samples to all of the pads inside your sampler, it offers your sampler the input potential of an MPC...once you glue or bolt it somehow to something solid (it's too flimsy and light in comparison to an MPC, and the pads won't work correctly in response to your taps until you do), it offers incredible control over dynamics, and very fast triggering of samples which a keyboard can't compete with. Lots of fun. :)