There are many DJ/Producers colleges that make mashups in all kinds of styles and formats. mARKYbOY is one of those people who I recently met at an internet forum. He is very actively working on lots of mashup projects and with great results. He recently made a complete mashup of the latest album from Amy Winehouse.
I have this guide already for some time on the links page, but I think it is worth an additional blog posting.