http://en.wikipedia.org/wiki/Cadence_(music)
EDIT: In fact, this article plus this one is an excellent place to start if you're looking for chords to vamp on or inspiration for songwriting.
http://en.wikipedia.org/wiki/Chord_progression
The first link doesn't lead anywhere. Is it the official wiki page on cadences?
http://en.wikipedia.org/wiki/List_of_chord_progressions
If you list it by number of chords, the maximum is the Canon at 5 unique chords used.
And the chord progressions page says:
Although, as noted above, classical music has its cliche progressions these are seldom named and discussed: perhaps only Schoenberg among the authors of popular text-books of harmony has made some attempt to do so.
I was looking for a more updated book than that of Schoenberg's.
I see all professional musicians hearing a film score or commercial and immediately recognizes where they "stole" that tune from. Often the tunes are manipulated so the common public won't immediately recognize it as iterative. But every trained musician can do it without any effort (meaning going through some record database to find a match).