Rexa.info is search engine for the academic computing literature developed by the University of Massachusetts, Amherst Information Extraction and Synthesis Laboratory. Here's a brief summary of Rexa:
Rexa is a digital library and search engine covering the computer science research literature and the people who create it. Rexa aims to facilitate research progress and collaboration by providing efficient browsing, search, associations and analysis among papers, people, organizations, venues and research communities.
You have to sign up for an account to use Rexa, but in return you get to annotate and tag citations of interest.
[Via Stephen Glass]