Two of the better ones are dpreview and photozone. Both provide ratings to give you an idea of the product. Phonezone has a star system and dpreview gives a breakdown over a number of categories and then gives an overall rating. e.g Highly Recommended, Recommended, Above Average etc and the is the rub I've never seen anything get below Above Average.
Now I appreciate they can't review everything but what the hell is average? If you read the review to get above average is awful! It would appear that recommended is what I would think of as average.
Now photozone is German and in explaining its ratings gives the following.
Some of you folks may be a bit surprised by the "rather low" ratings in the verdicts here at photozone.de. This isn't really intentional but you're simply experiencing a cultural effect. Photozone.de is located in Germany and locally the word "average" means just that - reads: "average" is in between of better and worse. So this is strictly different compared to the more popular anglo-american style meaning of the word where an "average" is equivalent to about as bad as it gets. Now you may argue that this is confusing but remember that this may be confusing for you but less so for visitors from different countries (thus different cultural backgrounds). We at photozone.de do firmly believe that "feel good" ratings are pointless - it neither helps you to choose nor does it help the manufacturers to get better.
Now I come from an anglo-american culture and have felt the pernicious affects of this denigration of average. Give someone a mark of average at an appraisal and they get all upset. Replace it as good and they are happy. The fact that everyone else got good doesn't matter and the affect is the same doesn't bother them. Its madness!
Surely we've got to get away from this feeling that we are all "good". Its just not true and is totally pointless. The truth is that at somethings we are merely average.