CiteULike

CiteULike helps you manage your citations. It stores them for you on-line, and you can input them by visiting journal web sites they are affiliated with, by inputing them directly from BibTex, or by typing the entries yourself. You can also export citations to EndNote or BibTex formats. Finally, they offer a social feature in that researchers can share their citations.

http://www.citeulike.org/