Hi Azizi -- Sorry I didn't see your question in time to answer you, but I see you found a much more complete (and entertaining) answer than I would have provided, so well done you! The great thing about zipper songs is they're so repetitive, people can pick them up extremely quickly -- even if they've never heard 'em before. Which reminds me, a swell zipper song that (surprisingly) hasn't been mentioned here yet is "Where Have All the Flowers Gone?"

Another real doozie of a singalong is "The Mary Ellen Carter". OK, it's not one that non-folkies will be familiar with, but the chorus is fairly easy to catch on to and it's the kind of song that really inspires people and gets them going -- so if most of the songs you're doing are the kind that folks can join in on straight away, you can (once you get 'em going) prolly get away with slipping in a song or two that they don't already know and/or is slightly more challenging.

I'm assuming Dani is in the US, 'cos she mentioned the "Rise Up Singing" book, which I don't think has made it to other countries yet (at least, not in any great numbers).

Another fun thing to do (& that people enjoy joining in on) is to sing one well-known song to the tune of another (also well-known). A few that I know work: Amazing Grace, House of the Rising Sun and Gilligan's Island can all be sung to each other's tunes.