I have a ton of books on Northern Ireland conflict. The Best ones I have are
A great series by Henry McDondald, Jim Cusack & Jack Holland on the non-IRA paramilitaries which include.... "INLA - Deadly Divisions" I have both the 1994 & 2007 versions, the updated version of "UVF - Endgame" & "The UDA - Inside The Heart of Loyalist Terror" - Great books, I love all the little details about dates, times, places, how exactly an action happened etc... I don't like the political tone, but it's a very well written book.
"The Road to Balcombe Street: The IRA Reign Terror in London" by Steven P. Moysey - Very interesting book, badly written in that there's spelling mistakes on every second page, but even still a fascinating book.