Note: since Exchange 2013 has been released, Microsoft strongly recommends to use it, making Exchange 2010 obsolete.
Information about Exchange 2010 and Load-balancing
ALOHA Load-Balancer for Exchange
The fastest and easiest way to Load-Balance Exchange 2010 is the ALOHA Load-Balancer for Exchange: a dedicated interface, simple and quick deployments (in a few minutes).
More information about the product, on Exceliance website: http://www.haproxy.com/en/aloha-load-balancer-exchange-2010