try Fionn MacCool's at the 70 Esplanade ( there's 3 other locations as well). Every Thursday you can get a bottomless bowl of mussels for $9.99. Unfortunately, I haven't been there yet but I plan on going soon. mmmmmmmmmussels!
Starfish Oyster Bar & Grill on Adelaide just West of Jarvis. They've got Losbters, Clams, Oysters, Fish, and the obligatory steaks. One of the best seafood places in Toronto, and a comfortable diningroom too.