Having recently moved to Oakville, I've tried a couple of the thai restaurants and been sadly dissapointed in the food. The other night we went to Bangkok One on Kerr street. We had the Pad Thai and Panang Gai. Both great dishes.
Other great thai places...
Mississauga: The Thai Terrace (on Hurontario south of Square One on the east side) is fantastic. Great spring rolls here.
Central: Khmer Thai (St. Clair and Oakwood) my all-time favorite!
Satay on the Road & Salad King are also very good spots.