Khao San Road and its sister restaurant Nana are one of the two major oligopolies of good Thai food in Toronto. KSR always has a long lineup and it's not exactly pleasant waiting out on Adelaide St in the cold, but it's usually worth it when it's off peak hours (less than 30 mins wait). Try the Squash Fritters and the Khao Soi, which I believe is one of their signature dishes.