Many enterprise clients rely on LDAP as their authentication and authorization provider for their websites. LDAP is used to store all of this information, the infrastructure already exists, so why not use it? There are plenty of reasons. So much so that I don't know if I can ever "recommend" a client directly integrate their web site with LDAP again.
There are countless load balancers available on the market. Some hardware, some proprietary, some hosted - there are too many options to enumerate. Instead, here is a quick list of some of the most popular open-source software load balancers and their advantages/disadvantages -
