I love Noodlehead.
Not only is it tasty Thai noodles at a cheap price (and BYOB!), but the decor is so cute and the resulting atmosphere is great. Seems a bit hipster-y, but fun. I want to take every guest who comes to visit me here, and so far, I have! The only thing I wish is that it had other Thai dishes also! But what they do have is done pretty well.
Solid place for an introduction to Pittsburgh. (Oh and PS: Cash only -- don't forget!)