As many have already mentioned Chez Piggy is a great restaurant in Kingston. I lived there for 5 years and returned for a weekend recently. The food is still great. Here are some other great spots to try.
1) The River Mill (be sure to look at both the dinner and lunch menus whenever you dine, since they will often be able to make things from either menu)
2) Curry Original
3) Pan Chancho - This is the bakery for Chez Piggy. They have the best fresh bread and cheese selection. Make sure you try the 5 year-old Cheddar Cheese. This is a great place to pick up a bite to eat at lunch or a snack anytime. Be sure to go early in the day to get the best selection of items.
4) Wooden Heads - This is the last kitchen to close (at least for good food) in Kingston. The pizzas are incredible, with a thin crust and excellent flavour. My favourites include the caesar salad and the Pizza with tomato sauce and Chevre (Goat's cheese). They offer one that is similar on the menu, but the added toppings don't do anything other than increase the size of the bill.