By far the best link popularity checker ever! This software not only allows you to spy on your competitors, but will actually tell you the PageRank of site where your competitors are listed.

Getting links where your competitors are listed helps you get listed where all of them are listed. The whole is greater than the sum of its parts - believe it.

Get this software, it's worth the investment.

This free backlink checker does a good job for small sites with few links. It typically crashes after it gets to about 500 backlinks. It claims to show Alexa ranking, but I have yet to see that field populate.

Backlink Checker 2.0 lacks Google PageRank data and is someone unstable. But if you're on a budget it will definitely make a difference in your link development strategy. After all, something is better than nothing right?