UkeTx's list is right on. BTW
16 tons does work.
My specialty as a performer is getting group participation. I am good at it. I will give some general guidelines then list my favorites.
I look for popular covers. The top two covers of all time are
Somewhere over the rainbow and
Silent Night.
FolkSongs are a winner all around. the simpler the better. If you sing a foreign language folksong its native environment People will quickly join in no matter how poor a job you do.
Katyushka works for any language group in the former USSR. Also in this group are any songs you learned at school or camp that you remember. Also Any song where the last line repeats as chorus. Songs where the last two lines of the verse repeat as chorus work too, but not as well.
Gospel Songs. Even Jews like to sing gospel songs. (no slight intended):
I'll Fly Away,
Amazing Grace
Sea Songs whether shantys of forebitters or tinpan alley:
What do you do with a drunken sailor,
Rolling Down to Old Maui,
I've got Sixpence,
Popeye the sailor man. Some of these are best done accapella.
Cowboy Songs:
Red River Valley,
home on the range,
ghost riders in the sky
Beatles Songs
Uncle Tommy's Favorite Singalongs
I've been Working on the Railroad
I'll Fly Away
Paradise - J. Prine
Oh Susanna
Jingle Bells
Heart of my Heart
Five foot two
Jambalaya
Katyushka
Gilligan's Island
La vie en Rose
This land is your land
Battle of New Orleans
Johnny I hardly knew you aka When Johnny comes marching Home
Mac the Knife
Home on the Range
Rolling Down to Old Maui
I know you rider
Ripple
Star of the county Down
Four Green Fields
Lumberjack Song -(monty python)
I'm my own Grandpa. - chorus only
Five Constipated Men
Wagon Wheel
Country Roads
Waltz Across Texas - Take note UkeTX