Load balancer hardware, software and configurations vary. Many load balancers are appliance based. This means they are physical appliances that perform the load distribution tasks. Others are software based and perhaps have client software on individual servers within a server farm.

Vendors

Foundry Systems
Cisco-Local Director
Radware-Web Server Director
Resonate-Central Dispatch
F5-BigIP
Coyote Point Systems' Equalizer E350