Canon EF 17-40mm f/4L USM Ultra Wide Angle Zoom Lens

This was my first "L" lense. Bought it for the 2005 Detroit Auto Show and now I have taken about 30,000 shots with it on a 300D and a 20D. Works prefect in every situation, but sometimes the AF is a little slow in low light. The AF assist beam from my 580EX fixes this problem. Images are extremely sharp, but barrel distortion is evident on some 17mm city shots with lofs of horizontal lines. Paid $679 and its worth every penny.
Its a great pair with my 70-200 f/2.8L.

For weddings I will start doing in 2006, I may look into the 16-35 f/2.8L to gain a little low light indoors speed.

This lens was my first "L" lens, and I made a great choice. With aperture set to f/8 or above, you can capture some pretty incredible shots. I recently shot some pictures of pumpkins and they practically pop right out of the picture. (I also did notice a surprising number of other folks using DSLRs, but none of em had L lenses, and I caught a few glances of people checking this lens out).
I'll be honest though. When I first got this lens, I was a little dissapointed because it didn't really seem to be that much better than the kit lens that came with my Digital Rebel. After using it for a few months now, though, I've come to realize just how wonderful this lens is, and it rarely leaves my camera. The only real con is that f/4 means you'll need a high ISO setting or a flash indoors. This isn't a problem so much with higher end cameras with better ISO processing, but with consumer end DSLRs it may be a bit problematic. Although odds are, if you're looking at this lens, you're probably not using a cheap camera to begin with!

Seems to be many who are having focusing and softness issues with this lens, I among them. Send it to be calibrated at the Canon facility in Calgary. After over a month of waiting, and then weeks of unreturned calls, I faxed the President of Canon Canada and got a reply in minutes. Said they'd accelerate my repair (this, after one month of waiting), then a week later, emailed to tell me they'd lost the lens. They did send my a cheque for less than replacement value in the end.

OTOH, many have gotten sharp, trouble free lenses, hoping you're one, because you don't want to ever send a lens Canon repair in Canada.