If you are still looking "A Secret History of the IRA" by Ed Moloney is a good place to start from the Republican side of things. I found Peter Taylor's "Provos, the IRA and Sinn Féin" to be informative. Both books are early 2000's so I'm not sure how they have aged with newer research.

While secondary 'history' books are really useful for an overview/synthesis of the period, I'd really recommend getting your hands on some primary sources and first hand accounts to really get an understanding and feeling for the period.

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Eamonn McCann's War and an Irish Town is a very good read, as is Maria Maguire's To Take Arms. I'm afraid I don't know any that are more useful for the Unionist/Protestant viewpoint, but they're a good start to get into the period none the less.