4. Pink Floyd
Reunions are supposed to be pale, pathetic retreads of the past, but when the classic Pink Floyd line-up took the stage together for the first time in 24 years at 2005's Live 8 it was pure magic. For years Waters and the rest of the band had been touring separately as they sniped at each other in the press, but for these four songs they were again the same unit that brought stadiums of 70,000 people to a stunned hush in the Seventies. Back then they turned football stadiums into fantasy lands, with airplanes flying overhead and pigs hovering above the stage. In 1980 they brought it to the next level by building a wall onstage. Sadly, Richard Wright's death in 2008 makes another complete reunion impossible – though relations between David Gilmour and Roger Waters have thawed to the point that a brief run of shows is no longer a completely impossible thought. It's just very, very unlikely.