Here is a list of photography links and resources that I personally find very useful when researching for a new/used Canon lens of all grades, and when looking for good new/used Canon lens on the Internet. Please share with me if you find anything that should be on the list too! (info@canonlens.ws):

Photozone.de
A frequently used site when I am looking for the different properties/pros/cons of a lens (i.e. sharpness, vignette, barrel distortion). Comes with very detailed analysis of a wide variety of Canon lens, with each review giving ratings on the optical, mechanical, price quality, pros and cons on the aspects of the lens.

URL: http://www.photozone.de