Depends on your needs, dude, like how many simultaneous inputs you require. someone is selling an Akai DPS12 in the classifieds for cheap and that can be nice although... I'll leave you to research a bit on that.
Of course, the Korgs, Rolands and Yahamas are nice, as are the cheaper Zooms, but my beef with these machines is that you can't swap out a converter for something better and the software... well, you live with what you have until they stop updating the firmware. Buit in fx are adequate for demos, but don't go expecting to make your master on these boxes.
That said, use any that does what you need. Some even come with drum patterns, like the Korgs (D8 I think?) For 40k you should be able to get a good box, but stay away from old technology like zip drives. If possible go for those that write to memory cards, and if possible, one that writes to .wav or mp3 so you can edit in your pc later.