A member just asked about this valuable resource: The Permissions Group, Inc. is a copyright and permissions consulting company with more than 20 years of experience negotiating rights and permissions. Infringement can be a costly mistake, even if it is done unintentionally. The Permissions Group, Inc. specializes in the negotiation of text and photo rights for the use of copyrighted material in and for all media.

One of my clients used their services earlier this year. His book was filled with quotes from famous people. All but one quote was in public domain. The one that wasn't in public domain was a lyric from a song. We were strongly advised to change it (and did).

http://www.permissionsgroup.com/