The good folks at the Center for the Study of the Public Domain at Duke University put together a depressing list each year of what would have gone into the public domain under copyright law if the law prior to 1978 remained in effect. You can check out this year's unfortunate list of works seized from the public in a retroactive one-sided renegotiation of the deal the copyright holders had with the public. These works should be in the public domain, and they're not... and the public got nothing in exchange for having these works taken away from us. Pulling from their writeup, here are just a few of the works that I thought you might find interesting:

The thing is, with the list of works from 1955 above, when they were all created, the maximum term of copyright of 56 years was a perfectly acceptable trade-off for those creators. They got their monopoly, and they created their works. What I can't understand is what the logic is in extending those rights retroactively. Clearly the incentive to create was fine as it was. Why should it change after the work was created?