The pentatonic scale, a 5-note scale, is the basis for countless folk songs around the world. Here's an explanation of the importance of the pentatonic scale in an Orff classroom:
The music used in the classroom is based on the children's own heritage with a combination of folk and composed music. Here in America, our classrooms are multicultural. Orff philosophy embraces the folk music of all cultures. They are almost all in the universal pentatonic scale. (Five note scale - separated by whole steps.) C Pentatonic would include the pitches C D E G A. This is the most common scale used in Orff because it is easily used with the Orff instruments. (from http://www.classicsforkids.com/teachers/training/orff101.asp)
Ai Hai Yo
Aia o Pele i Hawaii
Arirang
Alabama Gal
Al Citron
All Night All Day
Bickle Bockle
Bought Me a Cat - lesson ideas
Buck-eyed Jim
Camptown Races
Chicken on the Fence Post
Cotton Eye Joe
Dinah
Ding Dong Diggidiggidong
Doctor Foster
Ducks in the Millpond
Ezekiel Saw the Wheel
Fine Brick House
Fukien Boat Song
Git on Board
Goin' Upon the Mountain
Great Big House
Great Mornin'
Green Mountain
Goin' Down to Cairo
Hambone
Jim Along, Josie
John Kanakanaka
Old Dan Tucker
Rattlin' Bog
Sakura
Shake Them 'Simmons Down
Song of the Dragon
Sun Don't Set in the Mornin'
Swing Low, Sweet Chariot
Teddy Bear
Who Built the Ark
Zo-san
I like this book by Cristi Cary Miller. It has some great songs in it. 
