My brother and I have often had a great time thinking of as many songs as possible which follow a certain chord progression, e.g. 1, 4, 5, 4, 1, (very common).. as in Wild Thing, Stand (REM), Walking on Sunshine (Katrina and the Waves for those who ave to know), Louie, Louie, and the list goes on. It's great for busking, because you can seamlessly go from one hit to the other.