Some useful websites:

• Wild Welfare - Founded in 2012, Wild Welfare is a UK registered charity working globally to improve welfare for wild animals living in captivity.
• Enrichment.org - The Shape of Enrichment, Inc. is a non-profit corporation that offers a variety of services to animal care professionals worldwide.
• Animal Enrichment - Disney's animals, science and environment animal enrichment program.
• AZA - Association of Zoo and Aquaria: Animal Care Manuals

Other useful sources:

• A general Google search will bring lots of links to other organisations
• Pictures of animals using enrichment
• Youtube has examples of some amazing enrichment designs!