Before adding the load balancer make sure you stress test your app to know where the bottleneck is (CPU, memory, disk, network etc). See if you can't double your throughput by some cheap upgrades e.g. if you are CPU bound on a single core, you'll buy yourself some breathing space by upgrading to dual or quad core processors. If you are CPU bound but have loads of free memory consider caching expensive queries in RAM for a few seconds.

I only point this out, as load balancers and additional servers can be expensive.