great suggestions,
I usually use Cubase with Groove Agent vst (a drum machine that works like a virtual instrument). The sound quality is excellent/professional, you have many (50-60) predefined styles (shuffle, hard rock, pop, grunge.....) and is easy to use. Only problem is the price, probably you konow how to try it by P2P emule?
http://www.bornemark.se/ga/ (both products are from steimberg)