Rough Trade is one of my favourite place to hang out when i'm in Williamsburg. Located in the central williamsburg, it's the cool place to hang out in between concerts in the hood or late night. You can enjoy some shows there or come shopping for some music goods.
They carry a nice selection of new vinyls, cassettes or cds. The store offers nice listenings stations as well as a guitar's pedals corner where you can try very cool sounds.
Coffee and drinks can be enjoyed as they recently opened some bar in the store.
Located in Dumbo/Brooklyn, The powerhouse Arena is one of my favourite bookstore. Could spend hours there looking at almost every art/music books.
Large selection of books in amazing huge industrial space. They also hold some events and small exhibitions.