If you are looking to load balance your Apache servers, don't bother looking for a new piece of third-party software. If you're running version 2.2 or higher of Apache, it has load balancing already built-in with the mod_proxy_balancer package.

This module gives you a full-featured load balancing package. It's a front-end proxy that load balances between any number of servers, it maintains sticky sessions, it supports traffic-based load balancing, along with hot spares and hot swaps. It even comes with a web-based console tool where you can manage servers on-the-fly.

Best of all, it's free!

You can read all about the mod_proxy_balancer package here: http://httpd.apache.org/docs/2.2/mod/mod_proxy_balancer.html