Pros Superb optics
Cons Hefty and on the pricey end
Summary I have the EF 70-200mm f/2.8L IS. The f/2.8 aperture is as wide as you can get for a tele zoom (you need a prime lens if you want a wider aperture). The IS version works great in low light action handheld shots. The optics are superb, as good as it can get for a zoom lens. I bought this lens to take photos of my fast moving 3 year old, and it works great. However, the size can be intimidating to some people. When I use it in the children area of the mall to take photos of my son, the security came and thought that I was a pro taking photos of children without parental permission. The weight is not a problem. I carry this lens along with my Canon 30D, EF 17-55mm f/2.8 IS and my Sony HDR HC3 camcorder all day without problem. The price is also on the hefty side, but the lens is worth every penny. And this lens will outlast the camera body.
Pros Image Stabilization, Fast Focus
Cons Low battery on the 10D causes an error at times
Summary This lens is incredible! Many, many more keepers. Only thing I have noticed and not all of the time, when the Canon 10D battery is running low this lens may cause a communication error between the body and the lens forcing you to shut down the camer, slightly dismount the lens and remount and then it works. It's pretty rare but for the price you'd think it would be flawless.
Pros Sharp photos at all focal lengths and most f-stops.
Cons A little expensive but probably worth the money
Pros I photograph highschool football under the lights at night hooked to a digital rebel. Great shots, freeze action, no flash.
Cons The buttons on the lens move to easy I have turned the I.S. off several times by accident