I have one of the Yamaha DD-9 drum thingies (without the circuit bending switches):
And it is about the third one of this type that I have owned. They haven't broken or anything, but I gave one to a friend and one to a guy who needed it more than I did. 100 patterns, controllable tempo, and you can usually get them in a steal off of eBay.
They are super portable, and you can play it like a digital bongo, if that is your thing. Sometimes it is my thing...
The other device that I liked is the Zoom rhythm box, but it is not plug and play. Something like the Yamaha box you just pick a style and play.
Oh, there is another cool thing where you can switch patterns in mid song and switch back. It can be really cool. You can kinda play it like a beatbox. My first one had a feature where it would only switch at the end of the bar (delicious odd meters) and I basically had an entire band project built around that thing. I didn't know it would be so hard to replace
