Load Balancer for MySQL MASTER MASTER Replication
As you already have a running Master-Master replication, here a tip for the load balancer: I use HAProxy

It is a free software balancer, needs very less system resources and is quite easy to configure.

A tip: Install 2 loadbalancers with keepalived or keep in mind that you just created a critical bottleneck.

I use the setup keepalived + 2x haproxy + 2x master-mysql for 9 months now and I only noticed one problem with pdo_mysql - you can see my problem here: https://stackoverflow.com/questions/26871221/slow-pdo-mysql-mysqli-with-haproxy

There is also a small example config (in the example it is a hot standby master)