1. Metacritic. This site compiles reviews for movies, DVD's, TV shows, books, and yes, music. I only use it for music. Click "Music" at the top, and then on the left sidebar you will notice a few "Best of..." links. Below that is an "Upcoming and Current Releases" list in alphabetical order. Click "Sort Them By Score" and see the list in order of best to worst according to combined reviews.
Now you can click artist by artist and see which CD is reviewed and then read blurbs from each reviewer. A number of the reviews contain a link to the full, external review.
This site isn't perfect. When reviews don't contain a number score, Metacritic will assign it a number on a 100 point scale so it can be put in the tally. Some review sites and mags end up giving a slew of 100 ratings, and that just doesn't work. So you may find inflated scores here and there.
Another problem is that there are artists and CD's I would love to see reviewed that aren't given any attention. That can be frustrating.
Nonetheless, this is still my favorite site for discovering which CD's I want to look up on iTunes to see if it might be worth buying. I also have this site as a favorite on my Treo cell phone so I can use it when at the music store.
2. Peruse good music magazines. You may want subscribe to a good magazine like Paste (my personal favorite) or Under the Radar. They will have a number of reviews in each issue. I can't afford to subscribe to much, so I spend a few minutes shuffling through the pages in the bookstore to see what stands out. And I'll pick up an issue here or there to read about artists I'm interested in.
A downfall of depending on one magazine is that they might not like something you think it great. Or maybe it will be the other way around. I rarely read one review before picking up a CD.
3. Read music websites. A number of magazines put their reviews online. Good to check those out. But there are sites that focus only on the web. Some of the ones I like are Pitchfork, Dusted, and Coke Machine Glow.
4. Podcasts. Many of the music magazines and websites have their own podcast highlighting artists and CD's. I've tried out many and find them all helpful in different ways. Currently I subscribe to KEXP's Live Performances and NPR's All Songs Considered.
5. Internet radio. Sites like Pandora (easily my favorite) and Last.fm can be very helpful in finding music that fits in the style range of music you already like. So you tell them what you like (each site has a unique way of doing this) and they play similar music.
This doesn't always work like you want it. Sometimes I think, This isn't anything like the music I enjoy. But you can skip songs and move along. I still find these sites worthwhile.