Where do you start? (this could keep ABers going all night!)
If the party is quite soon then get down to your local library a.s.a.p. and see what they have. Check out books such as the Guinness hit records book (usually in the reference section at around 780 ) Check compilation CDs and if the lucky person is about to be 50 then I guess you will want to concentrate on the late '60s-early 70s period. 1970s was a great decade for cheesy party music, if for nothing else!
If you want to play a song for every year of the person's life, then I suggest you post again and allow the collective genius of ABers to help you with suggestions.
You might also check your local charity shops for LPs put out by K-Tel, Ronco, etc......