Canon EF 24-105mm f/4L IS USM Lens

I own this lens, and it's perfect for my Canon EOS 5D. This lens has a great range for a standard walk-around lens. Even with a crop factor camera the range is pretty good, just a little more telephoto.
On the wide end, there is some vignetting. I use a UV filter on this lens permanently. If I put my polarizing filter on too, it will actually clip the corners at 24mm. I just make sure to zoom in a tad if I use my polarizing filter. Also at full width there is some distortion. You can correct for this in Photoshop or other programs.
I purchased this lens from bhphoto.com another respectable site is adorama.com Please beware of using ultra-cheap stores. If you're tempted to use someone else, do yourself a favor and do a google search for "company_name fraud" where company_name is the name of the company you're tempted to use, and see what comes up.
This lens is similar to the 24-70mm F/2.8L, but with the IS. The image stabilizer that Canon puts out it great. Assuming your subject isn't moving, you can get some amazing shots at even quite long shutter speeds. I've taken shots with 1/4 second shutter times that you'd swear were taken on a tripod. (Well, at that sort of time, I do prop the camera up against a building or something for additional support, but it's still quite amazing.) If you're trying to decide between this and the 24-70 like I was, you have to ask yourself this: "Does one stop of light outweigh the IS?" Personally, I like the IS better. If I'm looking for bokeh I'll use my 50mm prime. (definition for newbies: bokeh is the blurry foreground and background in shots. The more open your lens, the more this effect shows. This is not always bad. Many fashion/portrait shots do this intentionally.) I don't use a tripod too often, so the IS buys me more. I can take landscape shots at F/8 - F/16 without a tripod. Nice!
Zoom dial is nicely firm and smooth. It's got a nice feel to it and doesn't slide in or out on its own. Other lenses start to move out while you're walking around, due to gravity because the lens typically points down when the camera is hanging on your neck.
The lens is pretty big compared to cheaper consumer lenses. This doesn't bother me. It fits quite nicely on my 5D, but looks huge on my Rebel XT. You want to spend a large percentage of your camera budget on the lenses. I cringe when I see people buy a very very expensive camera like the 5D, then put a cheapo $100 lens in front of it. Sure it'll still take good pictures, but you're sort of wasting the extra quality on the camera body. If you're on a tight budget, I would recommend spending less on the body, and buy this lens. Look at the 20D or 30D for cheaper bodies, or the 10D if you don't mind used. Your lenses will last for decades if taken care of. You can upgrade your camera body quite easily.
I'm very happy with the quality of this lens, it's quite sharp at all apertures. Check out the forums at dpreview.com for additional comments.
Good luck and happy shooting!
-Porter
oceanofapathy@hotmail.com