There are a number of boards that already provide that kind of feature set.
One problem that arises, is that the bulk of these boards are using legacy interfaces and will be difficult to work with on newer operating systems.

I know of one '52 board which has a full USB 1.1 implimentation that you may want to look at. It includes a complete USB interface as well as PC side software support so that you may write your own applications which manipulate it.

If you would like more information, feel free to email me at seiyahoshino@attbi.com