CiteULike is web-based tool for organizing academic papers. It is also a social bookmarking site that uses tags to organize and find related content, similiar to del.icio.us or flickr. I've been using it for a while now, and I am addicted. It is a very useful tool that helps me be more productive. My favourite feature is also the simplest: To post a paper, you find the paper on the publisher's web site, then use a bookmark. CiteULike automatically fills in all the bibliographic details and adds it to your library. Another useful feature is that you can export citations in BibTex format, which makes it easy to use your bibliography with LaTeX. Overall, it is a good example of what a web application should be: simple, easy to use, and responsive. If you are curious, you can browse my CiteULike library.