The second post songs are really known to all Germans, but young Germans may not really like them anymore.

Alanabit has mentioned the songs acceptable to younger and all age Germans (I would have recommended his first two as well).

Hannes Wader may be not known enough for them to sing along. 99 Luftballons is a good choice, Blinde Katharina (what a beautiful song) is too unknown, dat Du min Leevsten is also know to South Germans.

(BTW, Alan, regarding the grammar of Marmor, Stein und Eisen bricht, it is correct German as I have learned just a few weeks ago. Before that I would have called it wrong. Gold und Silber lieb ich sehr, kann's auch gut gebrauchen is an old German student song with the same construction. Rule: If some nouns are mentioned that all come from the same group and are meant to designate one particular property of that group, in this example "all that is hard and strong" the singular may be used. But I didn't know that just weeks ago)

Wolfgang