AllMusic puts their reviews online, using a 1 (worst) to 5 (best) star rating system, and providing both a review of the record and recommendations as to favorite tracks. It may not be definitive, but it reviews a tremendous number of artists in a wide range of genres, and is certainly a good place to start. It is also available in paperback (which I have).
Fuzz Acid & Flowers is a book by Vernon Joynson containing detailed information on 5400 (relatively) obscure US acts playing 60s psych and garage music from 1964-1972, as well as of compilations. In addition to identifying the band’s personel and its discography, it also contains reviews of the music they played. When I first wrote this post, it was available online. Alas, no more. Now you’ll have to find it in paperback, (which I have), which has pictures both of the groups featured, and of some of the albums discussed, as well as a chart giving a rough guide as of the date of publication of the value of some of the vinyl discussed.
Trouser Press has also put their reviews online. This covers again more obscure performers active during the 70s, 80s thru to the mid-90s. Reviews of the artists covered and their music are provided, offering a wealth of opportunities to explore bands less popular but nonetheless worthy. The site’s faqs provides that the site puts online the first 4 editions of the Trouser Press Record Guide, published in the 80s as well as the Trouser Press Guide to 90s Rock, published in 1995. These guides, which I have in print, introduced me to many a fine act, including the Last (their first record is great) and the Baracudas, among many others.
Rolling Stone has published a series of record guides over the years that review and rate records. The various Guides (which I own) are not online, but a description of them, the records they rate and how and who rates them, can be found on Wikipedia. The rating system goes from 0 stars (worst) to 5 stars (best). While the books are not online, Rock List.net has published lists from the various editions that list the 5 star records from each of Rolling Stone’s guides. I’ve linked to the list from the 1983 edition. You can find links to the others to the left of this list. To read the whole review, you’ll have to buy the books (well worth it). Rolling Stone does post online 500 Greatest Albums of All Time which contains reviews of the albums recommended and photos of their covers.
This ones going to be much harder to find. In the late 70s/early 80s David Shutt published a 78 page record review of 60s punk/psych records titled Journey to Tyme: A discography and interpretive guide to 1960s punk / psychedelia. Short on words, this publication contained a discography of numerous Texas punk/psych bands, and a rating on a scale of 1 (lowest) to 4 stars of the singles they made. If Shutt gave it 4 stars, it was a superb record. His taste was impeccable. Yes I have a copy and have relied on it to buy records in the past (pre You tube) and so can you if you can find it. No sighting of it online as of this writing.
1001 Albums You Must Hear Before You Die, edited by Robert Dimery, contains reviews of – you guessed it – 1001 albums from the 1950s to 2000s of various genres. Given the wide range of years it covers, it is bound to introduce you to something good you do not know. I for example found the Libertines this way, an excellent band, as well as Elliot Smith, among others. It also recommends the individual tracks on an album it likes the best. While the book itself is not online the list of albums it recommends is.
Robert Christgau’s Record Guide The 80s contains reviews of 3000 records from the 80s by Robert Christgau, a rock critic published regularly in the Village Voice. He grades records on an E (lowest) to A+ (highest) scale. Besides having good taste, he also knows how to turn a phrase, making his reviews enjoyable as well as informative reads. Covers all releases by the artists reviewed in the 80s. And its online at the link provided to boot, so you won’t have to buy the book like I did. But I bet he’d like it if you did. Oh, and he has lists (also on the site) with recommendations for your core collection, as well as lost but not forgotten treasures.