humanstxt.org

An initiative to know the creators of the website. Contains the information about humans to the web building.

tools.seobook.com/robots-txt/

Generate effective robots.txt files that help ensure Google and other search engines are crawling and indexing your site properly.

www.seobook.com/robots-txt-vs-rel-nofollow-vs-meta-robots-no...

This is a table of the three type of Nofollow compared against each other

www.askapache.com/seo/seo-with-robotstxt.html

Very nice tutorial dealing with the robots.txt file. Shows examples for google and other search engines. Wordpress robots.txt and phpBB robots.txt sample files.

stackoverflow.com/questions/14196801/sitemap-url-in-robots-t...

This thread tells you how to references your sitemap in the robots.txt