This isn't on the Web, but Band-in-a-Box has a really comprehesive selection of styles (and they are editable) and it is very simple to create standard midi files with any of the parts, down to the drum tracks--I use them a lot--just import them into Musicshop(which I prefer to the more complex and more recording rather than composer oriented Vision program)--however BIAB is available in both MAC and PC versions

Truth be told, you should teach your students how to write those rhythm patterns themselves, because if they are going to learn to compose anything in any of those idioms, they have to know how to write drum parts, anyway--