- Stanford SULAIR Copyright Renewal Database covers renewal records for 1923-1964, a key period for many genealogy works. The database offers simple and advanced searching by keyword, title, author and registration dates.
- U. S. Copyright Office has online copyright renewal records from 1978-present. The search options are comprehensive.
- WorldCat Copyright Registry is a new resource, currently in Beta, which allows for collaborative input on copyright status for different works. The site is mainly geared toward library and institutional use, but anyone with an interest in the copyright status of a particular work, and a free WorldCat account, can add information to the item pages.
(As an aside, one of the most comprehensive tables on copyright status I have found is at Cornell's website. Very comprehensive, and covers the thorny foreign work/author/renewal issues.)