Mashups are one of the most contentious genres in contemporary music. At their worst they can be amateurish mixes of musical styles that were, frankly, never put together for a reason.
However, when handled with due care and attention, a mashup can be a beautiful thing. From Danger Mouse's Grey Album to more recent Girl Talk releases, the best of the genre doesn't simply cut and paste a vocal onto an instrumental, but fundamentally re-writes the work, in something more akin to sampling.
The latest example of this comes from British producer Seanh, whose Sadevillain project matches Sade and MF Doom -= a move perhaps inspired by Doom's very public admiration for Sade, as seen on several previous tracks.
One of the best tracks is "Silver Spoon," which remaps Doom's lazy drawl over a re-worked version of Sade's "Jezebel" to stunning effect.
Of course the best bit about mashups is that they, by their nature, have to be free. Grab Sadevillain here.