Below I've collected a few tests I've done on various lenses. Maybe they'll be useful, maybe not. If you want qualitative evaluations of Canon lenses, you can visit http://www.the-digital-picture.com/.

NOTE: I used the 4MP Canon 1D for these tests -- likely the sharpness of some of the lenses is beyond a 4MP Bayer sensor's capability to resolve detail. Bayer sensors are inherently unsharp due to the anti-aliasing filter and demosaicing algorithm (A Foveon sensor doesn't have these problems, but has color difficulties instead). Since I didn't sharpen images, they may seem slightly soft.

• Canon EF 24-70mm f/2.8L USM: Sharp even wide open. At the 70mm end, only SLIGHTLY soft below f/3.5. Fabulous lens!
• Canon EF 70-200mm f/4L USM: Slightly soft at f/4, better above f/4.5.
• Canon EF 100mm f/2 USM: Sharpness is unchanged with respect to aperture. Use it wide open with confidence!
• Canon EF 50mm f/1.8 II: Quite soft wide open. Wonderfully sharp above f/2.2! Great value!
• Zenitar 16mm f/2.8 fisheye: Fairly Sharp at f/4. Cheap ultra wide angle lens.