Following the blog posts on the life of a riff, this seems like a natural sequel. The badly named Axis of Awesome, Australia's most tolerated musical comedy trio, has pointed out what most musicians have noticed but not entirely thought through. A lot of pop music consist, at least in central segments, of a sequence of just four chords; D, A, Hm and G or a transposed version of these.
Although the trio might not be awesome in the original sense (as explained by Eddie Izzard - see above), they deserve credit for clearly and efficiently stating the point and compiling such a long list of songs, not to mention how they spread hope to lonely, unattractive but clever bachelors with a worn out instrument.
Here is their four chord song:
They could have done worse, wouldn't you say?