The Queen+Madonna stuff is great.
I'm not wild about the Queen+$0.50, and the Kleptones album is cool too but there are plenty of places to download it.
New York at Last will make the list, and probably the Queen+Barney just for fun.
Anyone know of other good ones out there?
Here's a couple for Radio Ga Ga:
DJ M.i.F - Drop It Like It's Radio Ga Ga
(Snoop Dogg vs. Queen) link
Instamatic - Burn Your Radio
(Leftfield vs. Queen and Public Enemy) link