In my opinion, Thai Gourmet has the best Thai food in Pittsburgh. Being Southeast Asian, I've had quite a bit of Thai food, authentic and not. Their food is authentic, and they say it is also family owned. I have only came for the $10ish lunch special. I don't know a better deal than that!
My go-to choices are the Red Curry with chicken (spice level 7) or the Pad Z-Ew with beef (spice level 5). They give plenty of food and I usually have leftovers at the end. I'm never disappointed, whether it be the food or the service.
The outside appearance of this place isn't the greatest, but don't be shy. Thai Gourmet is nicely decorated inside, and the food is surely going to keep you coming back.