OAIster 
A catalog of digital resources from open-archive collections worldwide, including theses and dissertations. Contains some 25 million records from over 1,000 contributors.
OAIster is a union catalog of more than 19 million digital resources from over 1,000 organizations developed by the University of Michigan and harvested using OAI-PMH (the Open Archives Initiative Protocol for Metadata Harvesting). Digital resources in OAIster include items such as:
-Digitized (i.e., scanned) books and articles
-Born-digital texts
-Audio files (e.g., wav, mp3)
-Images (e.g., tiff, gif)
-Movies (e.g., mp4, quicktime)
-Datasets (e.g., downloadable statistics files)