There are two sites that I really dig for lens reviews (notice I didn't say camera reviews). One of them is photozone.de, which seems to give a very good real-world perspective on how a lens will work on your camera & what it will (& won't) do for you.
The other one is lensrentals.com, which if you read this site needs no introduction.
luminous-landscape.com has IMHO the best impressions on the net of cameras from the user's perspective, i.e. how well they handle and how easy they are to use & travel with. It's also where I learned most of my fundamental photography technique, both digital and optical. There are other sites out there like digilloyd & reid reviews, but as long as photography remains a hobby for me I can't really justify sinking any money into a subscription to a review site.
Finally, if you really want to know how a sensor performs in low light, the astrophotography folks (clarkvision, thierry legault, etc) have excellent methodology for analyzing sensor performance.