The following mastery setup is a good general setup for any ability power carry or mage in the game. The Tier conditions are not known yet. In this guide i assume that they won't be changed, so summoners have to spend at least 4/8/12/16/20 points unlock Tier 2/3/4/5/6 respectively.
This can be the typical AP carry build in my opinion. So far we have spent 21 points. Use the rest on the Utility tree.
I think this setup is pretty good for ability power carries and will be used by lot of summoners. It gives more ability power, better cooldown reduction, magic penetration. Overall more damage.