There is the Alesis SR18... which is a cheep alternative..

However, most people use NI Maschine or the Akai 6MPC stuff, but they all require a computer for soundsource..



This video however shows the best available right now, and despite its age the Boss is still 3rd placed... The elekron looks to be worth a look, its on the number one spot and i remember quite some nice comments on it from NAMM