A serious Oracle WebLogic Server (WLS) environment including Oracle Service Bus (OSB) infrastructure should be set up with at least one load balancing device which acts as a real endpoint.
An absolutely professional product is the load balancing device of "Layer 7 Technologies, Inc.". Also they are providing a great XML gateway (Not all SOA and XML gateways are created equal. Over the past several years Layer 7 has established itself as a clear leader in the XML Gateway market for several reasons).
Actually you need a load balancing device and a XML gateway in such a SOA environment because soa security has absolutely priority! Many articles about Layer 7 Technologies and load balancing can be found here on zdnet.com.
Of course there can be a simple implementation with Apache's round robin software Principe. The you don't need any hardware load balancing device. But I think you run better and more secure with a hardware part.
Also I found some interesting blog article about "why not using a hardware load balancing device like Layer 7" here.
Whitepapers about Layer 7 :
Both Denial of Service DoS and Brute Force Attacks have existed for many years, and many network devices tout the ability to withstand them. However, most of today's DoS attacks target layer 7 (L7) by overwhelming applications with seemingly valid requests and Brute Force programs can send more than one...
Provide Layer 7 load balancing and content customization on Cisco content switching solutions This sample chapter, taken from Designing Content Switching Solutions, introduces the Layer 7 load-balancing technology.This sample chapter, taken from Designing Content Switching Solutions, discusses the...