Google “Angelika Milster” and “Katja Ebstein.” You can also go to www.footlight.com and do a search.
On Frank Zappa’s “Joe’s Garage” there is a song called “Stick It Out” where the first half of the song is sung in German and then the second half is the English translation.
Nina Hagen covered The Tubes’ “White Punks On Dope” as “TV-Glotzer.”
ETA: Terry Jacks did a version of “Seasons In The Sun” in German, but good luck finding it!
Pretty short list, huh?
I also have some remakes of their songs in German by Doris Day, The Everly Brothers and The Hollies. The Peter Gabriel “Melting” album mentioned above also has the German version of “Games Without Frontiers.”