Love Harbourfront especially in the spring & summer. While there's events, classes, exhibits throughout the year I personally think it's the best in the spring and summer as they have the outdoor market with food, clothing and trinket stands - not too mention free samples from companies.
I love that every weekend in the summer there's always some sort of festival or event to bring people out to enjoy. The Harbourfront folks seem to put in their best efforts to make the place entertaining and the weekend festivities are free! Fun and free, can't be beat!