anyone know any good ones that are decent to jam along to, for improv or whatever, practicing etc
I got myself a DR-880 not too long ago. Very pleased with it; programmable beats, a drummer can play one easily (at least mine can make it sound like the real deal), tons of pre-programmed beats, EZ compose for when you just wanna play, has a decent processor built inside.

I like to write all my covers to that thing, then lug it around and plug it up and it becomes an instant bassist/drummer.

Overall it is very easy to use. There are some advanced features that i have yet to get into, but for now i use it for generic beats and covers that i program in. Definatly worth the $400 i paid (slightly used).
i know of DFH but its expensive and you will need a program like Cubase to run it.