Reciprocal Link Monitor
http://www.coralpalms.com/software/reciprocal-link-monitor.html

Website owners love to swap links. The problem is that many websites will put your link up for a short period, and then take it down when they don't think you're watching! While their sites are benefiting from your traffic, you're getting ZERO in return! Now, you can EASILY know when your links or banners have been removed from their sites!