This week's book giveaway is in the OCPJP forum. We're giving away four copies of OCA/OCP Java SE 7 Programmer I & II Study Guide and have Kathy Sierra & Bert Bates on-line! See this thread for details.
I dont see that very often having a load balancer for the database.
I think the best way when you have multiple database instances is to use the built-in clustering features.
From your application server this is transparent, everything will happen as if there is only one database instance.