No mention of Gamerankings?
It's like the Rotten Tomatoes of video games...
I don't use Gamerankings that much, but I thrive on Metacritic. Looking back at games that I've played in the past, Metacritic's score aggregations have been almost spot-on. It's also great that they link to specific reviews to see where the reviewer was coming from if you didn't already know.
In terms of non-aggregate reviews though, I guess I trust Gametrailers the most. Game Informer is second, but I realize they inflate their reviews, so I take them with a grain of salt. IGN and EGM are also people who I trust for reviews, but they're not the first people I turn to.
Honestly though, with a lot of games I'm interested in (like if I'm a fan of the series or something) I won't even look at the reviews except for the fanboy aspect of "MARIO GALAXY HAS A 97 METACRITIC AVERAGE TAKE THAT GAYLO 3 LOLOLOLOL" which I almost always keep to myself.
In terms of scores, I like to think that the scale is from 50 to 100 rather than 0 to 100. With games I find that reviewers usually tack on 5 points for the game just being able to work without an ***-load of glitches, and I don't mean like glitches that you have to work hard to find, I'm talking glitches that are very major and obstruct the ability to just play the game. Because of this, I usually only buy games with scores above 90, with 85 being probably the lowest I'll go. This may make me sound like kind of an overly choosy prick, but if I just bought every game with a score above 75 I'd be spending upwards of $200 a month. By being so selective, I can basically guarantee that I'll be getting my money's worth. The only times this method doesn't work is if the game in question has <20 hours of gameplay, but most reviewers would knock off a few points because of that.
Also, I've found that a general rule on handheld games is to add 5 points to the final score to give it a better scale in measuring up to console games, ie. a handheld game with a score of 85 is as worth buying as a console game with a score of 90.