Evasion

The Creature or Character can avoid even magical and unusual attacks with great agility. If he makes a successful Reflex saving throw against an attack that normally deals half damage on a successful save (such as a red dragon’s fiery breath or a fireball), he instead takes no damage. Evasion can be used only if the creature is wearing light armor or no armor. A helpless creature (such as one who is unconscious or paralysed) does not gain the benefit of evasion.

Classes with Evasion as Class Ability

Monk (2nd Level, Ex)
Ranger (9th Level, Ex)
Rogue (2nd Level, Ex)
Swordsage (9th Level, Ex)