We searched on "body fat percentage" and browsed through Yahoo!'s Health category to turn up many different estimations of healthy body fat.
Most sources agree that the human body requires a certain amount of fat for good health. Fat helps regulate body temperature, store energy, and cushion and insulate organs. The percentage of body weight that makes up this "essential fat" is around 4% of body weight for men and 10% for women. Beyond that, there's a somewhat wide range of what is considered a healthy percentage of body fat.
According to an article from Medscape.com, the American Dietetic Association recommends that men have 15-18% body fat and women have 20-25% body fat. Healthy male athletes might be as low as 5-12% body fat, and healthy female athletes could be as low as 10-20%.
Dr. C. Everett Koop's site, ShapeUp.com, breaks down healthy body fat ranges by both gender and age. Men under 39 years of age should have 8-19% body fat, and women under 39 years of age should have 21-32%. Older men may range from 11% to 24%, and older women may range from 23% to 35%.
Health Check Systems quotes the American Council on Exercise and says men's body fat should be 6-25%, and women's should be 14-31%.
Doctors increasingly use the Body Mass Index (BMI), not body fat measurements, to determine whether or not a person is overweight. BMI is based on a mathematical formula using height and weight that estimates overall body composition. The National Heart, Lung, and Blood Institute offers a handy BMI calculator and tables so you can see where you stand.