SEO is a competitive game, and more importantly, traffic generation online revolves around referral traffic. Seeing who links to your competitors is invaluable data.

My favorite backlink analysis tool is part of the MOZ tool suite, and its located at //www.opensiteexplorer.org . You can see which links are providing the most SEO value or link juice to your competitors websites, and you can analyze all sorts of other nifty tricks.

I would also encourage you to setup Google Alerts, or some other media monitoring service to see when your competitors brand gets mentioned or linked to so you can find how they are getting their traffic, and hopefully steal it.

Happy Hunting.