Roc is a free online music creator that's entirely browser-based, point and click - no musical ability required. It looks like most other loop creators, in that you choose from a decent selection of instruments (there are 10 drum types alone), assign them to tracks and then click to create notes.

Editing options are unsurprisingly on the basic side, but Roc is a lot of fun to use, offers plenty of scope for creativity and lets you save the results as an MP3 file when you're done. (The instruments are all Creative Commons-licenced, too, so whatever you create can be used in any way you like, no royalty restrictions to worry about.)