I went out for a walk with the EOS 50D and a Sigma 17-70mm f/2.8-4 lens that's been sitting around. I'm not sure if this lens will be good enough for general use but it's constructed nicely with a useful focal length range and is a bit faster then the usual kit lens.
One way to overcome a less than stellar lens is to bracket photos for high dynamic range processing. HDR images have a processed quality to them that masks the sharpness or contrast of each of the component images. Someday I'll do a comparison with a really good lens and a really cheap lens to see how similar the HDR images are to each other.
Here are three examples from this morning at Peebles Island State Park. All are HDR files from 3 +/- 1 ev bracketed images. Processing was with HDRSoft's Photomatix Essentials and it's Painterly preset. The local rivers had been high after recent rains and melting and have receded a bit, leaving ice and debris on some flat areas.