Sunset Clouds

The impressive thing about this is the detail in the cloud structure (although this might not be quite as apparent in this image which has only 3% of the original pixels and is JPEG compressed to make display on the Internet practical). Clouds tend to be quite "fuzzy" but this picture shows some real sharpness and fine detail.

Also the quality of the Canon lens is demonstrated by the areas where the black trees in the foreground touch the brightly lit clouds - many lesser optics would show colour fringing, and other problems there, but in this photo the edge is perfect.