Just came across this on another mailing list - would be interested to
hear if it's any good...
http://scholar.google.com/

Official blurb: "Google Scholar enables you to search specifically for
scholarly literature, including peer-reviewed papers, theses, books,
preprints, abstracts and technical reports from all broad areas of
research. Use Google Scholar to find articles from a wide variety of
academic publishers, professional societies, preprint repositories and
universities, as well as scholarly articles available across the web"

Matt