Thai Princess is a great option for Thai food in the downtown area. This spot offers affordable lunch specials that are in big portions - average cost is approximately $10 for a lunch dish.
Every time I come back to Toronto, I find myself stopping here by myself for lunch on a Friday. I must say, it gets completely packed very quickly during the lunch rush (12pm-2pm). The best time to go is after 2pm to ensure you get a spot and less time spent waiting for your food to come out.
The service is always friendly and great. Always making sure you are enjoying your meal and re-filling your water. The only issue that made me take a star away is the feeling that they want to get you out of there AS SOON AS POSSIBLE. Every time that I've gone there (busy or not), they would put the bill on my table right after I take my first bite. Not a big bothersome for me, but still not the most pleasant feeling of being rushed.
Overall, great location (easy TTC access), great service, and absolutely amazing food.