Google Research Search API

From their site: The University Research Program for Google Search is designed to give university faculty and their research teams high-volume programmatic access to Google Search, whose huge repository of data constitutes a valuable resource for understanding the structure and contents of the web. Our aim is to help bootstrap web research by offering basic information about specific search queries. Since the program builds on top of Google's search technology, you'll no longer have to operate your own crawl and indexing systems. We hope this will help enable some useful research, and request only that you publish any work you produce through this program for the academic community's general benefit.