I have long been a fan of the website The-Digital-Picture.com as a fantastic source for in useful review of Canon cameras, lenses, and accessories. The reviews presented are the perfect length to provide an great overview of the equipment, without requiring hours of reading to get the idea. Each review also provides a brief comparison to closely related equipment with a discussion of why the buyer might want to choose one over the other.
For example, Canon has three wide-angle zoom lenses that, on the surface, have very similar specifications (EF 16-35mm f/2.8L, EF 17-40mm f/4L, EF-S 17-55mm f/2.8 IS, EF-S 18-55mm f/3.5-5.6 IS); however, even though their focal length ranges are similar, these lenses are all extremely different have have very different target markets. The reviews for each of these lenses includes discussion about some (but not necessarily all) of the related lenses. This information is gold and it becomes very easy to narrow in on a couple of the lenses as the likely preferred options.
The site has recently been updated with a brand new Lens Specifications and Measurements comparison tool that allows you to directly compare lenses to easily see the differences in height, weight, diameter, and many other physical properties. In the past it has been very difficult to get this kind of information at all, never mind finding it in one place. Finding it usually required wading through multiple review sites, online retailers, and the Canon website.
If you are a Canon shooter and you haven’t been to The-Digital-Picture.com, you should go there right now!