Zotero
Zotero is a tool for organizing research information, including web pages, documents, and books, and generating bibliographies and reference citations in standardized formats. It has been released as a standalone program and as a browser plug-in for Firefox, and there are also add-ons to interface with popular word processing software to allow references to be inserted in your own documents. With Zotero connected to your browser, you can capture web pages, saving a "snapshot" of the current page (HTML, images, etc.) and storing reference info such as title, URL, and date accessed; for some sites, including Wikipedia, it can also find additional citation information from page metadata. Other references can be created by entering the ISBN of a book or the DOI of a paper, which get looked up to find the bibliographic information. You can also add files from your computer, which you can then open from Zotero later.
A variant version, CitationStylist, adds multilingual support, and also got into a bit of conflict by adding support for legal citations of the Harvard Bluebook style, which has its copyright vigorously protected by its owners (even though they're a coalition of nonprofit educational institutions) who don't want to allow any third-party derivative works, despite the fact that its citation style is specifically required by many courts for citations in legal filings.
