+1 on NYC Velo and RideBrooklyn. I've had good experiences in the past with both, mainly for mechanical work on my road bike and fixie. Always friendly and courteous. If I was in the market for a new bike I wouldn't hesitate to give either shop my business if they dealt a brand I was looking for. Just outside NYC, if you do the Piermont / Nyack ride, Piermont Bicycle Connection has also given me good mechanical service in the past, and has a pretty decent sized showroom, by NYC standards.