Any modern dual core laptop will have sufficent compute power.
If portability, like taking it to class is required, then an ultrabook is the way to go.
But, the graphics capability for gaming will be limited. It should be sufficient for strategy games such as civ-4, but not first person shooter type games.
If you need fast action gaming, then you want a laptop with a strongish discrete graphics chip, and they will be more expensive and less portable.
If price is not much of an issue, buy a laptop with a SSD, or replace a stock laptop drive with a SSD. The performance difference is remarkable.