Vielen Dank! The suggestion of 99 Luftballons is good--several young Germans mentioned it but at the time I didn't know the lyrics, and it's easy to sing. Everyone seems to know Marmor, Stein und Eisen bricht (though I agree that's it pretty awful), so that'll go into the list. For an older crowd, Auf der Reeperbahn, with the chorus I heard in a St. Pauli bar:
Auf der Reeperbahn nachts um halb eins
Ob Du Maedel hast oder Karlheinz
along with some of the older songs suggested by Genie. I can sing several old Marlene Dietrich songs, but they don't seem to get a response from Germans, young or old, don't know why.