Check out Nancy Cassidy
Nancy, author of the fabulously hilarious Chicken Lips, writer of KidsSongs and multiple award winner! From her biography:
Nancy Cassidy, a singer/songwriter/past PTA President/mother-of-two adolescent boys/wife-to-one-husband/and all around active woman has delighted audiences of all ages over the past 30 years.
And The National Institute of Environmental Health Sciences (NIEHS)http://kids.niehs.nih.gov/music.htm#index
You ask WHY NIEHS would have such a collection of sing alongs and put so much effort towards hosting all those midi files? In their words:
Why Do We Offer the Sing-Alongs?
Music is an important part of our "environment" and it can affect your health, but NIEHS has primarily included this sing-along section for educational purposes.