Link Building & Tracking:

These tools are essential in order to find out who is linking to you, how popular those sites and links are and how well search engines are indexing you.

Yahoo Backlink harvester - http://www.linkhounds.com/link-harvester/backlinks.php
This simply lists all of the domains that are linking to your site with some additional links to whois, cached pages etc.  

Market Leap Search Engine Saturation - http://www.marketleap.com/siteindex/
This tool gives you a quick summary of how many of your sites pages have been spidered and indexed within the major search engines. A link popularity checker is also available showing how many sites are linking to you.

Link Popularity Checker (Software) - http://www.advancedlinkmanager.com/
This affordable software shows how many links come to your site and creates a chart showing the increase of links over time. This software is easy to use and has extra features which allow easy result reporting.