DxO Side by side lens
That site looked like a good resource to bookmark.... until I noticed they only list Canon and Nikon mount lenses.
That leaves the Pentax, Sony and Olympus users out in the cold....
"The Digital Picture" is a relatively poor resource anyway, since they only test a lens with whatever camera body was the latest thing when the lens came out, with no updates of the tests with newer camera bodies. So if you want to compare lenses that weren't introduced damn near simultaneously, you end up with usless comparisons (i.e., different resolutions, different sensor tech, etc.). This is a particular issue for 3rd party lenses, which are usually tested in only one mount, making comparisons with any other camera makers' lenses useless.