Kassie - When my tomatoes get blossom end rot I sprinkle about 1/4-1/3 c Powdered milk around the stem and rub it into the soil before watering. It works well.
Blossom end rot is caused by irregular watering. Dry soil disrupts the regular calcium intake by the tomatoes roots, thus causing blossom end rot. The milk will help increase the calcium but you need setup more regular watering to completely avoid the problem. Bone meal is another organic additive that helps.