Revspin.net collects community-based reviews and ratings of table tennis equipment. It is the most extensive site of this kind that I know of.

TableTennisDaily also has a community-based "Equipment Review Centre" although isn't as extensive as Revspin.  

The Paddle Palace experts have developed useful rating tables for rubbers and blades (click on the "comparison chart view" button)

The TT Blades Database in one of my favorite TT-equipment webpages. It provides information about the ply composition of blades and the wood types used in the production of TT blades.

While simpler in its design, the StumpfOf site also provides information about the composition of blades and serves as an excellent supplement to the TT Blades Database.

MyTT forum member "h0n1g" maintains an informative blade frequency table. In a nutshell, the hypothesis is the higher the blade resonance frequency, the stiffer and faster the blade. While not fully correct (e.g., balsa blades have very high pitches, but aren't necessarily fast), this data collection is still informative.  

The Rubber Sheet and Mass and Size Database, which is maintained by MyTT member "haggisv", provides information about...well, rubbers. 

The TableTennisDaily team publishes some of the best known video-based TT reviews, which are always worth a watch.

TTGear Lab prides itself as being an objective Table Tennis Gear Laboratory. I especially like their scientific approach when analyzing blades.

TT-spin is a German-based TT equipment review site that I enjoy visiting. Marcel's writing style resembles mine a little bit. His equipment photos are gorgeous.

Also, I recommend you pay attention to any reviews from "yogi bear" that he posts on the MyTT or TableTennisDaily forums. The are always thorough and informative.

The ITTF periodically publishes a List of Approved Racket Coverings (LARC). New entries on the LARC provide a hint as to which rubbers might soon be released. You can view the newest list (right) or download the complete 2010-present list.

Table tennis forums are a great source for community-based in-depth TT-related information, but it can be a rabbit hole and time sink!

The MyTableTennis forum has been my go-to forum for a variety of topics, and I currently serve as one of the moderators there. It seems to emphasize the North American space. 

TableTennisDaily is another great forum, which seems to be more international in scope.  

OOAK (One Of A Kind) forum is yet another interesting forum, which contains particularly informative blogs on alternative rubbers, i.e., pimpled and antispin rubbers.