Search Engine Journal writer Ann Smarty talks about how exploration of competitors' backlinks can give you an idea of your competition's link building strategy and help you with keyword research among other things. She provides some tools for how to do this. The details are in the Search Engine Journal post, but the tools outlined are:
What's your favorite link analysis tool?
Forum discussion continues at Sphinn.

Comments:
Joost de Valk
06/10/2008 06:04 pm
My own :) <a href="http://yoast.com/seo-tools/link-analysis/">SEO Link Analysis</a> :)
David Cheong
06/10/2008 06:39 pm
Sorry to mention this, but i noticed the no.1 link backlinkwatch is actually pointing back to this website :). I normally prefer using the google link search to analyse backlink. Just have a look and test on the backlinkwatch. A great tool which i think webmaster should have. Thanks David Cheong
redorb
06/10/2008 08:45 pm
Why no mention of Yahoo search exlporer? we all know its the most accurate
Newbie
06/11/2008 10:53 am
These tools are great, but none appear to be able to tell me the location that the backlink is pointing to... Apparently SEO Elite can do this - does anyone have expereince of this product/know of another that can do this?