There is a drum machine called "rhythmcomposer" that I made for PD available at http://www.pure-data.org/community/patches

It will play up to 8 layers of any patterns of any length in any subdivision of the beat with any sound, calculate the loop point of the various patterns, display the patterns and count out the beat cycle. I use a CD of professional drum samples to go with it, which for obvious copyright reasons can't be included with the patch, but can be purchased at any music store.

-Miles Okazaki