Martial Power
A book released by Wizards of the Coast that expanded on the martial classes (Fighter, Rogue, Ranger, and Warlord) in Fourth Edition Dungeons and Dragons. It has new abilities for each class up to level 30 as well as feats for each class and new paragon paths and epic destinies.
Oh, and before you ask: /tg/ generally considers the book to be good and worth buying (well, since you are a 4efag anyway).