I purchased a Yamaha DJXIIB Groove Machine in the January sales, from the Maidenhead branch of Dixons of all places. For some reason they were selling them for £99 so I grabbed one!
I must admit it looks a bit of a toy, with the gimmicky scratch pad, but the strong point must be the drums which are excellent especially when mangled with the on-board effects unit. Programming your own patterns is also a bit of a doddle (although does require a computer with Cakewalk).
Definitely worth checking out.