Aaron Wall (of SEOBook fame) has created a free open source link analysis tool. It relies on the Yahoo! API and is limited in the number of requests in can make in a day, so he offers the script for others to mirror on their sites. I have now added Link Harvester on SEO Scoop to serve as a mirror for the tool. You will find the link to the tool in the navigation under SEO Scoop Tools.
Link Harvester has a lot of nice features. It shows you unique domains linking to the site, including the IP address and unique C block addresses of the links. It also isolates links from .gov, .mil., .edu and .ac.uk domains as these links are likely to have greater impact. It includes links to archive.org, whois, and Google cache near each link. In addition, it allows importing to .csv (Excel) format. Put your competitor's url in the form and find out just how strong his backlinks really are, or use your own url and discover where your weakness lies. Basically, it is a great little link analysis tool that you just need to try to appreciate.
The tool also links to the source code, so you can download it and run it from your own server, or supply a mirror for others to use as well. Thanks, Aaron, for such a cool SEO tool.