One thing I like to do for sing-alongs is songs that have enough times between lines for you to call out the next line.

WHAT THE HECK DO YOU CALL THAT KIND OF SONG, ANYWAY????

Examples are:
Just A Closer Walk With Thee
Singin' In Tne Rain
On Top Of Old Smoky
Ripple (3 out of 4 verses)
When The Saints Go Marching In


(Drawing a blank on others, but they're out there.)

Genie