Harrington on Holdem is the standard text for tournament players. Comes in three volumes. 1 and 2 are essential, 3 is a book of problems and you can get by without it, if you are on a tight budget.
In addition to the HoH series, there is Tournament Poker for Advanced Players by Sklansky, and Tom McEvoy, alone and in collaboration (Cloutier, Daugherty), has ritten nearly a dozen books on the subject of tournament play.