Consider the six basic emotions: anger, fear, joy, disgust, sadness and surprise. These are common across all the races in all the lands. Heroes and villains alike feel exactly the same emotions as a simple innkeeper and his family. What differentiates the heroes and villains from the innkeeper is in how they harness their emotions.
Think for a moment about the various types of adventurers you see, and reflect on how emotions are employed in their lives. Barbarians, with their raging strength are obvious users of anger, but so is the ranger who dedicates her life to eradicating goblinoids. Bards make their living playing upon the joy and sadness of their audiences, and any rogue worth his salt is a master of surprise. Necromancers and other like-minded wizards rely on disgust and fear for their powers, while paladins stand at the opposite end of the spectrum to oppose them. Clerics, druids and monks use a combination of these emotions in their daily lives, be it through communing with a deity, with nature, or while immersed in self-reflection. These people are not ruled by emotion, rather they harness it, turning it into a powerful tool which grants them nigh-unlimited potential and power.
The pages that follow detail emotion-based feats, prestige classes, magical items and spells that I have seen or discovered in my travels. It is my hope that you, dear reader, will learn to harness the power of raw emotion and use it to better the world.