I think Le Scaramouche hit something with his list--truth be told, not so many people know the old folksongs as know the hits from the 70's. A number of years ago, I went to see a David Bowie in Concert and then, a couple days later, Joan Baez in concert--to my surprise, the Bowie fans sang along with every songs, while the Baez fans did not sing a long at all. My suggestions:

My Sharona
YMCA
We Are Family
One Toke Over The Line
Miss American Pie
Proud Mary
Mama Mia
Rose Garden
Song Sung Blue
Your So Vain
Please, Mr. Postman

Oh, and Scaramouche--I know what you mean--I lived in a neighborhood with both Eritreans and Eithiopians--they had great food, great music, and evil, evil liquor--