Current US law extends copyright protections for 70 years from the date of the author’s death. (Corporate “works-for-hire” are copyrighted for 95 years.) But prior to the 1976 Copyright Act (which became effective in 1978), the maximum copyright term was 56 years (an initial term of 28 years, renewable for another 28 years). Under those laws, works published in 1954 would be passing into the public domain on January 1, 2011.So we could have seen both the The Fellowship of the Ring (1954) and the The Two Towers (1954) entering the Public Domain.
The 1950s were also the peak of popular science fiction writing. 1954 saw the publication of Richard Matheson’s I Am Legend (filmed three times in the last half century by Hollywood), Philip Wylie’s Tomorrow!, Arthur C. Clarke’s The Deep Range, Robert Heinlein’s The Star Beast, and the Hugo Award-winning They’d Rather Be Right by Frank Riley and Mark Clifton. Instead of seeing these enter the public domain in 2011, we will have to wait until 2050 – a date that, itself, seems the stuff of science fiction.
It's not just books, but films like Disney's 20,000 Leagues Under the Sea and Creature from the Black Lagoon that could be public domain.
Unless things change we'll have to wait a long time before these works finally enter the public domain.