Another One For Your Music Staff: Monkey Machine: Java-Based Drum Machine
What is it? It's a really simple drum machine, with lots of features. It's very easy to use.
You begin with a looping pattern -- by default it's 16-beat, but you can make it longer or shorter. Each position on the pattern can be set to "off," "medium," or "strong."
The TAP button you see there lets you set the tempo by tapping along with your mouse. Tap slow, and it slows down; tap faster and the BPM rises accordingly.
Once you've finished working on one pattern, you can add another pattern and start playing with it. Your two patterns will play in a loop, one after the other. Once you're done, you can export your beat as a MIDI file. You can also download existing beats that other users created -- there are over 11,000 of them
Link: Monkey Machine