You need a internal sequencer?
I just got me again a Roland R8m, 1U HE 19", lots a good kicks//snares/toms andso. Its somehow comparable with tr707/tr727 (most of the sounds are in it or sound very similar) andso...It sounds great imo, but I guesss you know about the Roland R8 series already 
Native Instruments drums I am not so fond of, it doesnt have that sound like a real drumrompler, although much is relying on the sourcesample material, I think that in a busy mix it doesnt hold, but thats my opinion, and maybe the Machine's audio-engine is better of that of Kontakt/Battery III
There arent much 19inch Drumsources besides the jomox airbase99, Drum/DStations and so, and they all focus on analogue TR sounds of the 808/909 series. A basic R8m has a lot of 80/90s digidrums onboard
Alesis DM4/DM5 is not much seen in electronic studio enviroments I think, I dont know much guys who have one, and the reviews arent that cheerful also..but thats personal taste I think.
There is also EMU Procussion module.