The US Green Building Council is a nonprofit organization "committed to a prosperous and sustainable future for our nation through cost-efficient and energy-saving green buildings." They administer the Leadership in Energy and Environmental Design (LEED) certification program, a worldwide effort with certified buildings in 135 countries. They are the acknowledged standard for verifying sustainable building materials and practices.
Of course, a building can be "green" without LEED certification. Here are a few resources: