http://science.discovery.com/science-technology/10-computer-viruses.htm
http://www.makeuseof.com/tag/history-computer-viruses-worst-today-case-wondering/
A bit more detail
http://www.cisco.com/web/about/ac123/ac147/archived_issues/ipj_6-3/virus_trends.html
http://www.zdnet.com/blog/btl/the-5-worst-computer-viruses/79014