http://www.martijn.com is a nice site to find more info on linux clusters, load balancing (lvs), high availability (ha) and shared storage solutions.
It has a lot information on load balancing, high availability, redundancy and shared storage.
Load balancing is the art of distributing tcpip requests to a pool of real servers. These might be directed to all kinds of services, tcp or udp. Mostly it is used for load balancing http servers, webservers. But mailservers, ftpservers and other internet servers can also be load balanced. Load balancing is made possible by the ip_vs module in the linux kernel. Several Open Source applications use the module for easy to use suites like the Piranha suite from RedHat or the independent Ultramonkey suite. Load balancers are often combined with high availability software because by using only one loadbalancer a Single Point Of Failure (SPOF) is created.