Where to buy key for Battlefield and Call of Duty?

Hey mates,
I would like to buy a key for Call of Duty: Modern Warfare 3 and one for Battlefield 3?
What is the best and cheapest place to go for?
I see russian keys sometimes, that are sold much cheaper, what about those ones?
Thanks!
Answer #1
Sorry but cant you just download them off warezz?, im non gamer by the way.
Answer #2
BAD IDEA! Your key could get nulled at ANY moment. If you want to play online, BUT THE GAME! DONT RISK A KEY WHICH COULD GET BANNED.
Answer #3
Cod: http://store.steampowered.com – Official store
Battlefield: http://origin.com – Official store.