Stanford has released a very slick Copyright Renewal Database. From their “About” page:
Copyright status of works published in the US between 1923 and 1963 is of particular concern, as it is dependent on whether the original copyright was renewed. Changes in copyright law have removed this question for works published after 1963. The Copyright Office has never made available in machine-readable form the renewals it received between 1950 and 1977, which would generally cover renewals for books published between 1923 and 1950. This has made it difficult for libraries and archives to determine which books are in the public domain.
Several organizations have taken steps to make the Copyright Office’s records more accessible. Most noteworthy is Project Gutenberg, which scanned and transcribed the printed renewal records. You can view their work here. This database builds on their work, making the text searchable by field in a single file. We are also grateful for the early efforts of Michael Lesk in the creation of this database.
Just to emphasize the point: this is finally one single place to search for these records. No more juggling two or three clunky tools. Yay!