Cod liver oil: This fish oil has a reputation for bad taste, but flavored varieties available today may make it more palatable. According to the Linus Pauling Institute at Oregon State University, which conducts nutrition research, a tablespoon has 340 percent of the daily value of Vitamin D and is also rich in omega-3 fatty acids, a fat essential to good health. Other types of fish oil are also high in omega-3s, but only cod liver oil contains vitamin D.