To anyone besides THUMPER who might scan this thread...I have to put in a plug for Native Instruments' Battery 3. (I seem to be the lone Battery 3 cheerleader here, LOL.)
If you are after more than acoustic drumkit sounds, Battery 3 is the best thing out there (especially for the cost). To be fair, I know John Emrich has been involved in a percussion add-on to BFD that (based on the sample demos) is really great...but it still doesn't have Battery 3's range of world/ethnic percussion. I'm talking about things like doumbeks, darabukas, tars, bendirs, riqs, tablas, ghatam, taikos, lion drums, and the entire range of African drums like djun-djun, ashiko, djembe, etc.
Battery 3 has a bit of a learning curve, but I find it fairly intuitive. Then again, I've been using MIDI software for years...so my perspective might not be accurate for the basic user. Battery 3 does come with over a hundred pre-assembled kits using the entire range of sample sets right out of the box...but at a minimum you have to set up the MIDI note mappings with the Zendrum to use them (since some kits have far more sounds than the Zendrum's 24 pads can use).
Finally, you obviously need a computer to use Battery 3...but it's cross-platform (Mac/PC). And I'd definitely state that 2GB of RAM is essential for reliability. In several weeks of wailin' away on my Zendrum with Battery 3, it's been rock-stable---no crashes, no hangs, no stuck notes, nothing.