"Blueberries are among fruits that are best recognized for their potential health benefits".
Sanchez-Moreno C. Cao G, Ou B, Prior RL: Anthocyanin and proanthocyanidin content in selected white and red wines. Oxygen radical absorbance capacity comparison with nontraditional wines obtained from highbush blueberry. J Agric Food Chem. 2003 Aug 13:51(17):4889-96

Antioxidants: Researchers at the USDA Human Nutrition Center (HNRCA) have found that blueberries rank #1 in antioxidant activity when compared to 40 other fresh fruits and vegetables.
Prior. RL, at al. J of Agric Food Chem. 1998, 46 2686-2693

Anti-Aging. In another USDA Human Nutrition Center (HNRCA) lab, neuroscientis discovered that feeding blueberries to laboratory rats slowed age-related loss in their mental capacity, a finding that has important implications for humans.
Bickford, P C. et. at Society for Neuroscience Abs. 1998, 24: 2157

High-ORAC Foods May Show Aging. .... ORAC, short for Oxygen Radical Absorbance Capacity. Early findings suggest that eating plenty of high-ORAC fruits and vegetables-such as spinach and blueberries-may help slow the processes associated with aging in both body and brain.

Top-Scoring Fruits & Vegetables ORAC units per 100 grams (about 3.5 ounces) Fruits Vegetables
1. Prunes 5770
2. Raisins 2830
3. Blueberries 2400
4. Blackberries 2036 
5. Kale 1770
6. Strawberries 1540
7. Spinach 1250
8. Raspberries 1220

http://www.ars.usda.gov/is/AR/archive/feb99/aging0299.htm

Disease Prevention - Blueberries day reduce the build up of so called "bad" cholesterol that contributes to cardiovascular disease and stroke, according to scientists at the University of Califomia at Davis.
Heinenen, L.M. et al. J Agric Food Chem. 1998, 46:4107-4112

Prevention of Urinary Tract Infections - Researchers at Rutgers University in New Jersey have identified a compound in blueberries that promotes urinary tract health and reduces the risk of infection. It appears to work by preventing bacteria from adhering to the cells that line the walls of the urinary tract.
Howell, A.B. and V Nicholl. New Eng. J. Med 1998, 339: 1085-1086