One that has not been mentioned yet is "Pro Studio Masters". If you are on their email list you will receive 4 or 5 mailings per week of new releases and remastered music from several genres all in hi-res. Almost all of the albums have samples of all tracks that you can listen to as well as read reviews. Even if you are not interested in hi-res, you can usually find the "red book" version.
Others have already mentioned record reviews in Stereophile and Absolute Sound. I take that one step further by noting all of the music used to evaluate equipment. I have found quite a bit of new-to-me music that way.