In addition to encyclopedias such as Credo Reference and Wikipedia, there are specialized encyclopedias that focus on one discipline or topic. The following are encyclopedias helpful for psychology topics.
2003. Macmillan Reference.
From the website: "Covering all aspects of death and dying -- biological, medical, social, sociological, psychological, religious, and philosophical -- the 2-vol. Macmillan Encyclopedia of Death and Dying also provides a deep historical and cross-cultural perspective through the ages."