Maintaining a bibliography can be a complicated and tedious task. BibTeX, and its younger cousin biber, are designed to simplify this task. With these tools you make a database of whatever entries you might imagine needing. When you write an article or a book, BibTeXwill search that database for whatever you happen to cite, and construct a bibliography for you in whatever style you need. It includes all of the traditional styles (MLA, Chicago, APA, and so forth), and many periodicals post files on their web to format BibTeX bibliographies in their house format. BibTeX and its siblings will also manage your in-line citations, in whatever form your text required, with all of the flexibility you might ask for.
BibTeX bibliographies can be created directly with any text editor since they are written in ASCII (or unicode). Some LaTeX-oriented text editors (such as AlphaX or Aquamacs) provide forms to hold your hand as you make BibTeX entries. But management of bibliography databases is easier still with BibDesk. (BibDesk runs on the Mac, but similar programs are available in the Windows world, and familiar reference managers like EndNote and Zotero can export in BibTeX format.)
BibDesk, which is available for free and included in the TeXLive distribution most TeX users already have, is a bibliographic management tool for BibTeX databases. It is much more, however, than a friendly user interface for entering BibTeX records. BibDesk is designed to connect to such databases as the Library of Congress catalogue and the Web of Science, and can import records from them. I have found that it can also import bibliographic records from the Brandeis Library OneSearch, and from databases Brandeis subscribes to, such as JSTOR, EBSCO, and the Arts and Humanities Citation Index. You can also use BibDesk as a “textbase,” annotating articles for later use as you you read them. Finally, you can attach the article itself to your database, so you can use BibTeX to keep local copies of your research materials organized.
Although BibDesk is designed to make BibTeX bibliographies for use in LaTeX documents, it can export files in EndNote and some other formats, and applescripts exist to import BibTeX bibliographies into Word documents, although the process is nontrivial.
Note: BibDesk only works on Macs.