This blog entry at Patent Pending examines the question of when copyright expire, and includes a chart summarizing the duration of copyright for various works based on their dates of creation:
“When Does a Copyright Expire, So I Can Safely Copy Something? This question is aimed at the duration of copyright. People often want to use a photo or some other copyrighted work, and wonder how they can be sure the copyright has expired. When a copyright expires, material can be lawfully copied.
The current law is that copyright lasts the life of the author plus 70 years. But a copyrighted is subject to the law that is in effect at the time it was created, and the laws have changed over the years.”