Player's Handbook 3... uuuh...

The book is misleadingly named, as only one new class is introduced for the Divine and Primal power source each. Instead, the focus is clearly on the Psionic power source, which introduces four new classes to the table: The Ardent, a leader who uses psionic magic to psychically influence the tide of battle; the Battlemind, whose psionics allow him to gain the tactical advantage that a defender requires; the Monk, a striker who uses harnesses psionic power to achieve total mobility and the Psion, a controller who brings down her foes through telekinetic assaults or psychic attacks.
The first thing you should know about the Psionic classes is that they introduce several new mechanics. The Psion, Ardent and Battlemind make use of power points – the quantity of which depends on a character’s level and is replenished after a short or extended rest – to augment their psionic powers, and have no encounter powers to speak of, save for some utility powers. Instead, they have a host of at-wills that can be boosted by these power points. For example, a Level 7 at-will called Ego Crush, allows a Battlemind to deal 1[W] + Constitution damage, and denies his target the ability to gain combat advantage until the end of his next turn. When boosted, it can be used as an opportunity attack or when maxed out, deals double damage against each enemy within a close burst.
All in all, the Psionic classes are exciting new choices for players. My only real misgiving is that it continues the trend in 4th Edition towards more book keeping. Between healing surges, daily item powers, encounter powers and daily powers and class features, there are already plenty of exhaustible resources to track without adding power points into the mix. Granted, previous editions had a disproportionate balance of resource tracking: fighters worried about little more than their next attack while wizards fumbled through reams of paper and post-it marked rulebooks to track casting times and mark spells to learn and memorize. Still, the Psionic classes are probably recommended for more experienced players. Thankfully, they aren’t just designed to be exotic for the sake of it, and are great additions to the game.