My top three to get folks to sing with me:
The Rivers of Texas/Down By the Embrass
Drive Dull Care Away (aka Contentment)
New Harmony (Craig Johnson)

Ballads with refrains: Lay the Bent/Binnorie,
Cruel Mother
Lowlands Away
Boys of Bedlam

If I Were a Blackbird, Black Velvet Band - so many in the Irish common repertoire that have easily memorable choruses.

So many Old time & gospel songs have grand choruses: Angel Band, Never Grow Old, I'll Fly Away, Cotton Mill Girls

Songs many were exposed to as kids at camp like Waltzing Matilda & You Can't Get To Heaven

I particularly like songs that use a repeat of the last few lines of the verse to make a chorus: When I was a Fair Maid, Rose of Allendale, Rani Arbo's setting of Crossing the Bar is SUPERB for this, the version of Renardine the Armstrong family sang, Thousands or More (the song, though there may BE thousands or more songs that work like this...)

Joanne in Cleveland
(who is working hard to have people sing things that are NOT in Rise Up Singing)