Well, I don't puch much weight on reviews; I rely more on the opinions of people on the boards.
But I do read a lot of reviews. I get Nintendo Power, GameInformer, Electronic Gaming Monthly, and Hardcore Gamer (and yes, I have gotten the majority of these either free or discounted anyways). I regularly go on Gamespot, IGN, and genre-specific sites (shmups.com or rpgfan.com).
I would say out of all of those sources, I trust Gamespot the most. They seem to write the most detailed, comprehensive reviews of games, without genre or system bias. After Gamespot, Hardcore Gamer is my second source, since they write solely toward the audience of hardcore gamers.
So when I want a game, I check the Gamespot review first, then if it hasn't already been reviewed in HCG, I might wait for the issue or check another site. If the scores kind of match (and are high enough for my standards), then I know the game was widely liked. If they are widely different, I'll check other sites and user opinions.