Trying to discover whether a work of art (book, movie, song, etc.) is currently in the public domain? The American Library Association’s copyright slide rule, should help.
[This] simple tool tells you whether or not you need to hunt down a rights owner to use a book, movie, song, or other work in a project. The surprising part? Often times, you don’t—not if the work was made before a certain year, and if the author didn’t follow through. Quick tip: Feel free to go nuts on anything published before 1923
Outside the US we have different laws, natch, though we are subject to these laws if we sample works that have a US copyright. It would be interesting to see a UK/EU version of this.