First of them is called Google Scholar and is maintained by errr… Google and the other one is named Academics and run by Microsoft. Both of them utilize the same idea – find all relevant sources of academic information about a specific subject. Great way to explore articles, publications and reference materials. Unfortunately some of the materials require paid subscription. I was little surprised to find that Yahoo! doesn’t have a similar service (yet?)
Hint: Academics does not work well with Firefox (no big surprise here…)
One last thing I would like to mention, that I use with pleasure – zotero. It is best described with the creator’s own words:
extension to help you collect, manage, and cite your research sources. It lives right where you do your work — in the web browser itself.