TeriLu, I'd go with rounds. They come in all ranges of difficulty and intricacy, they create their own harmony "automatically", and they're loads of fun to sing. There's "The Penguin Book of Rounds", and a wonderful little book called "101 Rounds for Singing", which I obtained many years ago from the publisher, World Around Songs, Inc., Route 5, Box 398, Burnsville, NC 28714. Some of my favorites are, in no particular order: "Great Tom is Cast", "Grasshoppers Three", "Hava Nashira", "Sweet Rest (Time Sends a Warning Call)", "Ride a Cock Horse", "Froh Zu Sein", "Rise Up O Flame"...Then there are the simpler ones, still good and fun: "Make New Friends", "Hey, Ho, Nobody Home", "Lady Come Down and See"...even "White Coral Bells". Have fun!

Aloha,
Mark