Action Point

Action Points are the method by which a character's Daily Powers are recharged. Each character has a gauge represented by a D20 in the middle of their Combat Action Bar. This gauge refills as the character gains more Action Points. When this bar is filled by the attainment of Action Points, a character's Daily Power is available for use. The use of a character's daily power depletes this gauge and a character must once again perform actions which grant Action Points to refill it.

According to the in-game tool-tips, each class can earn Action Points as follows:
 * Barbarian - Dealing damage and using encounter powers
 * Cleric - Healing or dealing damage
 * Fighter - Taking or dealing damage and using encounter powers
 * Paladin - Attacking foes and casting spells.
 * Ranger - Dealing damage and using encounter powers.
 * Rogue - Dealing damage
 * Warlock - ???
 * Wizard - Dealing damage

However, the tool-tips are misleading. For instance, Guardian Fighters can gain Action Points from blocking attacks, but do not gain Action Points from taking unguarded damage unless they have the paragon feat.

Barbarian

 * The first-tier heroic feat increases action point gain by 5/10/15/20/25% for dealing damage while you are.
 * The encounter power increases Action Point Gain.
 * The encounter power grants bonus Action Points when it kills a foe.
 * The encounter power does not grants bonus Action Points when activated.

Cleric

 * Charisma increases Action Point Gain.
 * The first-tier heroic feat increases action point gain by 1/2/3/4/5% whenever you use a healing ability.
 * The encounter power grants Action Points when its target dies.

Fighter

 * Blocking grants the fastest AP gain, and attacking while blocking grants more than cleaving.
 * Constitution increases Action Point Gain.
 * The first-tier heroic feat increases action point gain by 2/4/6/8/10% from Guarding attacks.
 * The encounter power increases your party's Action Point Gain.
 * The paragon feat allows you to build Action Points by taking unguarded damage.

Paladin

 * Charisma increases Action Point Gain.

Rogue

 * The first-tier heroic feat increases action point gain by 2/4/6/8/10% for dealing Combat Advantage damage.
 * The paragon feat Cunning Stalker increases Action Point Gain when Stealthed.
 * The paragon feat Action Rush gives your encounter powers a change to grant bonus Action Points.
 * The paragon feat Thrill of the Kill grants Action Points for landing killing blows.
 * The encounter power creates a decoy that grants Action Points to the rogue when it is hit by an enemy.
 * The class power increases Action Point Gain.

Wizard

 * Wisdom increases Action Point Gain.
 * The first-tier heroic feat increases action point gain by 2/4/6/8/10% when using powers on a controlled target.
 * The paragon feat grants 1/2/3/4/5% of your total Action Points when you land a critical hit.