A huge thanks to Dictum Mortuum for making his Wizard's Handbook, which I am going to blatantly copy for format purposes. Its just that well laid out.
Enchanters are the manipulators of the D&D world. They are all about controlling the people and monsters around them. Their spells focus on domination, charming, and controlling the course of battle. In addition, because of the nature of enchanters, an enchanter character will find himself having an easier time as a party face than other wizards. He benefits his spells by taking points in skills relevant to being a party-face, and many enchantment spells can be used to great effect in social situations. This is something to keep in mind when considering class roles for your game.
Enchanters are generally considered underpowered compared to wizards specializing in other areas or generalist wizards. This is primarily due to the fact that many creatures become immune/are immune to most enchantment spells later in the game. Early in the game, when your enchantments are mostly effective, pumping up the DC of your enchantment spells is somewhat difficult.
However, enchantment is a very flavorful school, and can be incredibly powerful if used properly. This guide will offer suggestions for those wanting to make an enchanter. Because of the difficulties the enchanter faces, designing one is different than designing a normal wizard.
This guide is designed around the controller archetype of the enchanter. This is a character who will keep the battlefield and his enemies under control at all times. Enchanters don't have to follow this route though. They can also be debuff masters. If an enchanter goes this route he will be focused on making his enemies as weak and pathetic as possible, so his friends can mop them up with ease. The controller works better if you have fewer party members, the debuff master works better if you have more party members. For the debuff master the only difference will be the rating of certain spells, such as confusion. For the controller these spell types are not ideal ... but for the debuff master they are great. Keep that in mind when reading this guide and, particularly, when looking over my spell ratings.
CantripN has contributed a lot to this guide, so thank you!
*Thanks to Surreal for the picture!*