A great guide to sour beers. These have been my obsession as of late and it is nice to know more about them: http://luckypeach.com/guides/guide-sour-beers/. Lucky Peach is a great magazine, totally worth a subscription.
The flavor profile of a sour beer can be very different from any other one. Many of the spots in the Cambridge / Boston area have been socking at least one sour beer recently, including Grafton Street in Harvard Square and Meadhall in Kendall Square. If you want a HUGE variety of beers to choose from, sour and non-sour, Meadhall has over 100 taps.