Mages

The three talent trees for Mages are Frost, Fire, and Arcane. Most builds you will encounter contain a large percentage of talent points spent in one tree such as Fire and then a much smaller amount spent in another tree such as Frost. To blindly throw all points into one tree such as Fire just for the sake of being a full Fire Mage is usually a mistake as all the talents in the tree you are mainly using are usually not completely beneficial to your situation and talents in another tree usually are.

What spec of Mage you choose to have depends on what kind of things you will be using your Mage for (farming, soloing, raiding, etc.) and what you like to do (AoEing, high single target damaging, or even freezing other PvPers :P). In my experience there isn't one single spec or tree that is the best, it really depends on the player and his or her skills and preferences.