Mage PvP guides often suggest to go deep frost or elemental (frost and fire). Those two specs are considered to be the most viable in PvP. However, there are a another mage spec which is a lot of fun to play, and is called PoM Pyro (Presence of Mind with Pyroblast) spec.
The PoM talent for mages makes the next spell instant, which means that you can cast Pyroblast instantly. Pyroblast is the most powerful spell for mages. With Pyroblast as an instant cast you can burst out a lot of damage in a short amount of time. In addition to PoM you have a spell called Arcane Power (AP), which increases spell damages by 30%. Those two spells in combination allows for a big burst of damage every 3 minutes. The rotation for this setup is as follows: sheep, fire one Pyroblast without PoM, then use PoM and AP together and fire a new Pyroblast instantly, use Fireblast and use Scorch if they are still alive. Most players will be dead after this combination, even good geared warriors.
There are different variations of POM Pyro. One version is to go deep arcane with AP, which can be seen in the image below. A second version is to skip AP and put more talent points in fire. Even though you can vary this spec the most important talents in this spec is Pyroblast and POM.
The downside to the PoM Pyro spec is survivability, as you have traded all survivability talents for the PoM Pyro spec. Another important downside is that PoM and AP have a 3 minute cooldown. This means that you can only burst this damage every 3 minutes. Even though this spec has downsides, it is a lot of fun to one shot players every 3 minutes.