Rosie's Yarn Cellar on Locust between 20th and 21st is probably the most well-known yarn store in Center City.
It’s a very small store, very claustrophobic. BUT, they have good service and a very knowledgeable staff, which makes up for the closeness of the walls.
The yarn selection is the best in Center City, but it can run a little pricey. You won’t find any Red Heart or Lion’s Brand here, but chances are, you'll find almost anything else.
They have quite a few patterns, pattern books, and knitting books, a wide selection of buttons, and a few other notions.
They offer a wide selection of needles, and they make an incredible effort to have something in every size, material, and style (dpns, circulars, straights) at all times. Some of the brands they offer include Inox, Addi Turbo, Crystal Palace, and Clover.
Overall, the store is worth a visit.