I don't trust "professional" rock critics (all the sites mentioned on metacritic), I just read some of their reviews by they don't influence me on music I purchase.
99% of them don't even give a f***k about the kind of music I like (pop/powerpop).
I'm more interested by music fans opinions, so sites like RYM or last.fm are the best.
I've discovered more awesome music on last.fm and RYM during these last two years than with magazines (on paper or on website) during the 30 first years of my life.
There's really no individual source I trust. Rolling Stone loves rap and hates new music that isn't rap or Weezer, Pitchfork has it's obvious biases, allmusic has ten thousand different writers and the particular tastes of the person who writes the review is a crapshoot.
I'd say my most trusted source is the friend I referenced in another thread. After that, maybe Pazznjop, though it also has it's biases. Popmatters maybe.