Minecraft
All Medal of Honour, Call of Duty, realistic army first person shooters.
Anything the Escapist advertises. This one's a bit odd but I spend so much time here watching and rewatching old videos that if they have adverts in the beginning (like for Fable III) I'll see it so many hundreds of times I get beyond bored of it and decide not to buy the game on principle that it's been marketed to me. This does extend to other sites but most sites I go to don't advertise videogames so much as things like Google Chrome or Bing.
On a related but non-videogame note The Princess Bride. I had it recommended to me by nearly everyone I know who watches movies, and although I have recently bought it a combination of my cynicism and the massive amounts of hype everyone gave it means I really wish I hadn't seen it. I really didn't enjoy it, but I get the feeling that I might have done had it not been so bigged up before hand, kind of like Halo 3. I enjoyed Halo 3, no mistake there, but I would have liked it more had it not been so hyped.