Sometimes you just need to go to the extreme - in this case it is really wide angle. In my old Canon film-camera days, I had the 15mm 2.8 fisheye which was an even bigger chunk of glass because of its speed.
Now that I have gone to the Pentax K100D camera, I was pleasantly surprised to see this 10-17mm lens was available. I was even happier because unlike the Canon lens, the Pentax is a zoom, so that not every shot has to be the distorted wide angle that you think of when you hear "fisheye". The lens goes out to the equivalent of about 26mm on a 35mm format, which is a very useful focal length as well.
The lens also allows manually tweaking the focus while in the auto-focus mode - something my 2 Sigma lenses warn against.
The only drawbacks to the lens that I see are that you can not mount a filter and the curved front element is exposed (same for the Canon). So, just use a little caution. And, unlike the old Canon, there are no rear filters either. Finally, for those who like to manually adjust the aperture ring - there isn't one. It's all set through the camera :-)
I could go on about the lens, but as they say, a picture is worth a thousand words, so I've posted a few photos in the Amazon collection.