CiteSeer: The NEC Research Institute Scientific Literature Digital Library
From the site:
CiteSeer is a scientific literature digital library that aims to improve the dissemination and feedback of scientific literature, and to provide improvements in functionality, usability, availability, cost, comprehensiveness, efficiency, and timeliness.
Rather than creating just another digital library, CiteSeer provides algorithms, techniques, and software that can be used in other digital libraries. CiteSeer indexes Postscript and PDF research articles on the Web, and provides the following features.