Don't go with alienware they are so overpriced and you can get better elsewhere.
I want to play stuff like TF2 and maybe a bit of CoD(sorry) at a pretty high fps and quality.
Ok so you want to look for laptops with these specs
Any i5 or i7 processor
A dedicated graphics card you can use notebookcheck to see how well the card will run certain games
At least 4gb of ram
However much memory you want if you can find one with an ssd that will make most stuff run faster a bit but its not necessary
A decent resolution I wouldn't settle for anything less then 1280 x 720
For what you want to use it for you could probably get one for around $750
The one rtewre123 found looks amazing for a laptop and the price is good as well.