I've been working on a Silverlight 3 drum machine/sequencer called Thunder, the first (beta) version is now available at:
http://www.dontcodetired.com/live/thunder/
It's a fully working version but the code base requires some re-factoring. Playback smoothness varies depending on the machine specs and how many instruments are playing at the same time.
Future improvements include the addition of more than 2 drum kits, the ability to use your own drum samples and attempting to improve the performance (although this seems to be limited by having to use a MediaElement to play a stream rather than an immediate .Play() method - hopefully in Silverlight 4 a lower latency sound playback mechanism will be introduced).
SHARE: