WhoLinksToMe.com – see who links to you in the blogosphere, and beyond

This is an excellent tool to keep track of sites linking to you. If you are trying to increase your pagerank or doing other traffic SEO, this is a critical benchmark.

WordPress Compressed All-Inclusive Ping List

This site keeps an all-inclusive ping list. If you are using WorPress and want to get the most traffic possible, keep up to date with this list of ping sites.