Yarn! is a decent yarn and knitting store located in Alameda. They are open 6 days a week (closed Mondays), and reserve Wednesday evenings for people to gather and knit and chat. They usually get a decent crowd. They do offer classes, though I've never taken any. The prices are pretty reasonable for them, and they have some fun topics, like how to make socks, or an intro to knitting class in case you want to learn.
The staff I've encountered has been friendly and helpful. And they appeared to be very knowledgeable about knitting and yarn. They seemed happy to answer my questions.
They carry a good selection of yarns including Rowan, Cascade, Anny Blatt, Koigu, Noro, Schachecnmayr, and a bunch more. Prices are reasonable.