OCLC has made basic and advanced OAIster search interfaces available. Access is free.
OAIster is a database of over 23 million records from OAI-PMH-compliant digital repositories, which was originally developed by the University of Michigan Library. Initially, OCLC made OAIster available only as part of WorldCat and as a FirstSearch database (these access points remain). (Thanks to ResourceShelf.)
Read more about it at "OCLC Makes OAIster Records Available through WorldCat.org," "OCLC makes OAIster Records Available through WorldCat.org to Ensure Long-Term Public Access to Digital Resources," and "University of Michigan and OCLC Form Partnership to Ensure Long-Term Access to OAIster Database."
