An Introduction to Genomics
Produced by the Joint Genome Institute at the US Department of Energy as part of its educational materials, this is one of the best basic primers available online.
It examines some of the technological applications of genomics - such as fighting disease, protecting plant life and harnessing "nature's technology" (for instance, outlining ways of using bacteria and other microbes to solve a variety of environmental problems, develop new energy sources, and improve industrial processes).
The article goes on to explain the biology behind DNA sequencing, describing the reasons for human differences and mutations, and how proteins are produced from DNA. It then compares the DNA sequence patterns of humans with a variety of other sequenced organisms, explaining why this is important.