Yahoo! Directory listing, Search Engine Bot,Google PageRank, Alexa Traffic Rank

Yahoo! Directory listing
This is similar to the ODP -- Google relationship. The Yahoo! directory is regularly crawled by the Yahoo! robots.

A new site has a greater chance of being included faster in the Yahoo! search engine if there is a link to this site from the Yahoo! directory. If you get your site is listed within the Yahoo! category closest to your site theme, this particular link will help your site move up.

Search Engine Bot
Search engine bot is a type of web crawlers which collects web documents to generate and maintain index for the search engines.

Google PageRank
Google PageRank is the measure of a page’s importance in Google’s opinion. PR calculations are based on how many quality and relevant sites across the Web link to this page. The higher the PageRank of the referring page, the more weight this link has.

Alexa Traffic Rank
Alexa Traffic Rank is a combined measure of page views and users (reach). This information is gathered with the help of Alexa Toolbar used by millions of Web surfers. First, Alexa calculates the reach and number of page views for all sites on the Web on the daily basis. Then these two quantities are averaged over time.