There's a couple of pretty good mash-ups making the rounds today. First CBC Music put all of the "doo doo doo"s and "whoa-oh"s that defined the 90's into one video called "The 90's Alt-Rock Vocal Hook Supercut":

And pretty good mash-up of The Beatles and Motley Crue. It's mainly the lyrics of "A Hard Day's Night" with the music of "Girls Girls Girls" but it's really well done.