AllMusic.com
A complete and current resource for recordings of all types of music including reviews, biographical information on the artists, historical information, ordering listings, and retail links.
Grammy Awards
A website dedicated to the annual Grammy awards including information about nominees and winners.
Metacritic.com
Compiles reviews from critics and publications covering film, music, video/DVD and games.
Rock & Roll Hall of Fame
The official site of the Rock & Roll Hall of Fame. Lots of music history here for kids writing papers, giving oral reports, etc.
In the past few years, Chicago-based Pitchfork.com has ascended to the top strata of indie music review websites. A rave review on Pitchfork has helped catapult several bands’ popularity. Recently, Pitchfork has expanded beyond news and reviews to also feature exclusive live music content. I have discovered several bands I was unfamiliar with reading Pitchfork.
Another Chicago area-based site, PopMatters bills itself as a “international magazine of cultural criticism.” You can find more than music reviews here, too. This site is highly recommended by fellow librarian, Tanya.
Dusted is based out of Brooklyn. They are run on a voluntary basis and do not accept advertising. Their website notes that their “reviewers live all over the country and vary greatly in age and background.” You will find a wonderful mix of reviews and feature articles on their site.
I think Cokemachineglow answers the reason why you should check out their website. “We like to think our staff collectively offers a unique twist on indie music criticism, with a somewhat democratic approach (hence the combined ratings, joint reviews, counterpoints) that makes our site more community driven. We’d like to think it results in a easy-going, friendly-in-a-complete-stranger-kind-of-way atmosphere—-something that makes our site stand out amongst the hundreds of other ‘wannabe Pitchforks’ and MP3 blogs, and something that makes us worth coming back to.”

Again, perhaps I should let the folks who write for this site speak for themselves. “At Tiny Mix Tapes, we provide both up-to-date and dated news, reviews, interviews, and articles on different genres in the vast music world, including independent releases, major label releases, and even self-releases. Tiny Mix Tapers are a bunch of over-achievers, and our primary jobs range from studenting, teaching, receptioning, cooking, and being full-time girlfriends of past models, to curing cancer and supplying Merriam-Webster with new words like ‘studenting’ and ‘receptioning.’”

Other Music is a fantastic record store in New York City that prides itself on digging up sublime, wonderful music you will want to hear that you have never heard (or heard of) before. Many times they are the only record store in the US that will carry a certain record (especially imported stuff), so their reviews are about the only thing out there. I recommend reading their weekly New Release Updates; there is always something good listed there.