This tool seemed a bit unimportant at first glance but then I thought that it might really be useful if you are looking for really good links!

If 2 or 3 of your competitors have a link from a site, well you need that link too!

This tool, the Common Backlinks Tool, allows you to enter up to 10 domains and get a list of the common backlinks for the sites.

The information does seem to slightly dated, but it’s very helpful after all!