BestFed has a great selection of everything you need for successful breastfeeding. They have the largest selection of nursing bras that I've seen and they are experts at helping you find the correct fit. They also sell shirts, pumps, slings and other accessories.
Everyone here wants you to succeed at breastfeeding and are more than happy to answer any questions you have. They frequently offer seminars and classes, or you can ask anyone working in the store for advice. They are all breastfeeding moms and can usually address any issues you're having.