I love the image quality I get with my Canon 40D and 17-40mm f/4.0 L USM glass. This combination really allows me to capture the beauty of a Texas sunset.
The Canon EF 17-40mm f/4.0 L lens is one of the most versatile ultra wide angle zoom lenses ever made, even when used with a 1.6 FOVCF (Field of View Crop Factor) body like my 40D which gives this lens gives an equivalent focal length of 27-64mm. The sharpness of this lens is nothing less than spectacular, especially given it’s very reasonable street price of $700.
Any professional landscape photographer will tell you that the third most important piece of equipment (body, lens) you can buy to improve the quality of your images is a good tripod. I use a Gitzo Traveller for stability and always set the 40D’s mirror lockup function (C.Fn III -7) to eliminate even the smallest vibration.