A new study of U.S. Eastern seaboard mercury levels in fish concludes that “Consumers selecting fish for ease of availability…would select flounder, snapper, bluefish, and tuna (tuna had the highest mercury value)…selecting only for price would select whiting, porgy, croaker, and bluefish. Flounder was the fish with the best relationship among availability, cost, and low mercury levels.”
If you like to eat out, the Audobon people have a nifty Seafood Wallet card. There are few peer-reviewed, published articles that give mercury levels: this one does. Fish is still a good choice, and there are free recipes to boot online, including those with fish to lower your cholesterol.