John Friedman wrote an excellent article on the Six Business Benefits of Sustainability. I picked it up at JustMeans, an online community focused on creating a values-driven economy. Here they are in summary form:

License to Operate (Speed to Market)

Cost Reduction or Avoidance

Market Opportunity/Advantage
(Impact of actions, and not intentions)

Employee Engagement

Access to Investment Capital
(From 1995 to 2003 assets involved in social investing have grown 40% faster than all professionally managed investment assets in the U.S.)