For my money, "There She Goes" is nearly impossible to beat in its pop perfection: from the tips of its chiming guitars to the bottom of its blissful lyrics, it simply doesn't get any better than this. If aliens came down and said that we had just shade under three minutes to justify our existence or we'd be evaporated -- well, I wouldn't necessarily suggest playing this song, but I might suggest someone put it on in the background while we boot up Stephen Hawking's voice synthesizer.
This song is 2:42, so John takes this as the duration to check, and finds it to be the winner. Chad agrees and everyone had fun sorting their iTunes list by duration (it makes for some interesting shuffle listening). I'm not a big pop collector, but in comments I did offer some pop tunes from the 20's through 40's, otherwise known as swing.