Your gamer probably likes to shoot stuff. Who doesn't ? If they don't have them all ready, check out titles like Call of Duty: Black Ops, Battlefield: Bad Company 2, or MAG. If you are shopping for a little one, be aware that some of these games are disturbingly violent and definitely not for everyone. If you have a sensitive gamer, check the ratings to match the player.
If you have a die hard RPG fan on your list, try out games like Oblivion, Fable 3, Fallout: New Vegas, and the Mass Effect series. Maybe you have a WoW-er in your house who didn't grab Cataclysm on the release date (unlikely), but if so, you'll make their season bright by allowing them to dominate a giant dragon in the upcoming months.
Does your nerd thrive on virtual action and adventure ? Look for Assassin's Creed: Brotherhood and Batman Arkham Asylum. The Force Unleashed 2 is on the scene, and since it's an exceptionally short game, its one that someone isn't likely to buy on their own but would still love as a present.
Do you or your loved one prefer to flex their brain more than that trigger finger? Take a look at Tomb Raider or Uncharted 1 and 2. Even games like Limbo, Portal, and Super Meat Boy all add high elements of timing and strategy. If your gamer plays puzzle games that aren't so fast paced, check out Brain Age or Professor Layton and the Unwound Future. (There's also Diabolical Box, or Curious Village if your gamer hasn't gotten into the Layton series at all.) The Phoenix Wright: Ace Attorney series is also a great hand-held puzzle game.
Already played all those games ? Don't forget accessories ! Rechargeable battery packs are a must. Even if they have some, they tend to slowly wear out so it could be time for new ones. Almost every gamer plays with friends online, make sure they have the equipment to do so. There are some nice options for high-end headsets for all consoles and PCs that range anywhere from $40-$200. You can also buy skins to help customize consoles and controllers with their favorite colors and characters.
And lets not forget stocking stuffers ! Buy some AAA batteries for those headsets ! A sweet mousepad for your PC gamer. You can even buy prepaid cards for Microsoft and Wii Points. Also keep an eye out for that worn cable that could be replaced or maybe a cool thumb drive to keep their game saves on for when they play away from home.
Here are a few straggling tips to remember. Used games are totally acceptable. I would much rather have two used games for the cost of a new one. But if you buy a used game, check the disc before you take it home ! Sometimes those games have been to hell and back and that person behind the counter doesn't always take the time to look at the condition of the disc as carefully as they should. Watch out for Game of the Year editions. Batman Arkham Asylum, Borderlands, and more come out with ultimate editions that contain all the additional content. Its so obvious; ask for help. Show the sales people that picture you took with your cellphone. They will be able to give excellent recommendations once they know what games your gift receiver likes to buy. Lastly, create a gamer if you don't have one. With the Nintendo DS, the Wii, the PS Move, and now the Kinect, everyone can find a game that they love to play.