Pittsburgh Guitars is a South Side institution, and rightly so. They have a reputation as the best repair shop in town, or maybe even in the region. They carry a wide array of brands and price-level of guitar and they are always friendly and willing to help. I have purchased 3 guitars from them and each time I have got a good deal on a good instrument. Their used selection is also pretty good at times (the turnover can be high so the selection varies dramatically) and the prices are always in line with what you will find elsewhere. They do offer lessons as well. The only con may be that the store is fairly small and quite cramped. There are many many guitars and amps available, but not much space to put them so when it comes time to sit down and try one out you might find yourself fairly cramped. Also be sure to check out the display in the back of the store which features a rotating display of 'not-for-sale' vintage instruments.
Pros: Friendly, knowledgable service, and solid selection.
Cons: Small store.