Wouter Hisschemöller has released the Euclidean Rhythm Generator (ERG) for Java 1.6. With this free MIDI-generator you can create amazing drum and percussion loops and play them back in Java with the built-in MIDI instruments. Hisschemöller also has a flash version available, which you can try right in your browser.
You can also send midi patterns to your sequencer. On our Windows Vista machine we tried this with Ableton Live and MIDI Yoke, a program that allows for the MIDI communication between Ableton and ERG. With MIDI Yoke we have some problems to get it running. Maybe MIDI-OX (by the same software maker) will work, but we still have to check this out.
It might work much better on the Mac, as this demonstration video shows: