A few days ago, Google engineer Jarkko Hietaniemi released the XML file
of all copyright renewal notices for books published in the United States between 1923 and 1963. The file is free and in the public domain, so I went ahead and imported it into a database-driven Web application, allowing you to do quick full-text searches through the records.
You can access it here: http://www.incopyright.org/
I should note that there is another similar online database
by Stanford University; however, according to the Google Book Search blog, the Google-based database contains "the best and most comprehensive set of renewal records available today".
Feedback always recommended.