Like most of my favourite tools halberd does one thing, and does it well. It tries to detect individual servers behind a load balancer. The idea behind it is not new, but this is the best put together tool that I have used. It even handles multiple A records right off the bat. It is a little short on documentation and the error messages could be better, but it's still a great reconnaissance/testing tools for pen testers and system administrators alike.
Grab your copy today from http://halberd.superadditive.com/