I think blueberries and pomegranates have the most antioxidants, but many other fruits and vegetables are rich in the little buggers. For apples, the Red Delicious is a sure bet - especially the peel:

Red Delicious, which account for 27 percent of U.S. apple production, has more than six times the antioxidants as the bottom-ranked Empire variety. Northern Spy was No. 2, followed by Cortland, Ida Red, Golden Delicious, McIntosh and Mutsu.

The skin of Red Delicious apples — the most common variety grown in the United States — contains over six times more antioxidant activity than the flesh, according to researchers at Agriculture and Agri-Food Canada... And in every variety tested, the skins of the apples contained substantially higher levels of antioxidants than the flesh.