I'm a big fan of Young's. It's a very authentic mom-and-pop Korean grocery store, something that's pretty rare in Pittsburgh. The place is smallish and definitely no H-Mart, but it has all the basic necessities of Korean cooking. Their kimchi is surprisingly good and the pork belly and chadol (thin beef brisket) I've bought there has always been tasty.
They also have a small produce section that I believe is cheaper than Giant Eagle down the road and is usually of pretty good quality. My only complaint is that they're often sold out of sesame leaves whenever I go shopping, or the one or two that are left over are limp. (Dunking them in cold water for 30 mins perk 'em right back up, though.)