IRLbot is a Texas A&M research project that investigates algorithms for mapping the topology of the Internet and discovering the various parts of the web. The crawler downloads random web pages (text only) and follows certain links to find other websites. The text of downloaded web pages is not distributed to the public or used for any non-research purposes. IRLbot is compliant with the robots.txt standard.
http://irl.cs.tamu.edu/crawler/