pitchforkmedia is the biggest online music review site on the web, and i'm guessing that most of you have probably all ready heard of it. It is a great place to go to read reliable reviews of new albums, because most of the journalists on the site are dead on. I think that the review of the new Jet album this year is particularly spot on.
The site is a great place to listen to new music for free, because they put up tons of streamable mp3s of bands that are more than likely going to become huge very quickly. There are also often a lot of great photos from concerts, interviews with musicians and filmmakers, and one of my favorite features is the annual 100 best albums of the year. Under the "best new music" category there is a comprehensive list of their highest rated albums, from most recent to least recent, and seeing as they put up about five reviews every weekday this is a good way to separate the Radioheads from the Jets.