What It Was: One of the oddest megahits of the ’00s, based musically by DJ Danger Mouse around an old Spaghetti Western theme composition and featuring Cee Lo Green, then known just as a soul eccentric and a former member of Goodie Mob, waxing poetic about the nature of sanity and what it truly means to lose one’s mind. The song was simply too good to ignore, and became a #2 hit, eventually getting named by Rolling Stone as the song of the decade.

What Happened Next: The duo had several more fun singles with even more fun videos, but never crossed over again like they did with “Crazy.” Cee Lo improbably went on to have a hit on his own on that level with “Fuck You,” though with just the one, he’s threatening to become one of pop music’s only-ever three-time OHWs, with Goodie Mob, Gnarls and solo. Danger Mouse continued to have success of his own, forming another superduo (Broken Bells) with The Shins’ James Mercer, and helping turn the Black Keys into rock stars on their breakout album Brothers.

Where Are They Now?: Danger Mouse is still quite in demand as a producer, most recently doing Norah Jones’ latest LP Little Broken Hearts and starting work on the upcoming U2 album, and of course you can catch Cee Lo a couple nights a week as a coach on NBC’s hit music competition show The Voice.