ISBN: Unique identifing number for books. Stands for International Standard Book Number.
DOI: unique identifying code for journal articles. Stands for Digital Object Identifier.
WorldCat: a centralized website of library books including the authors, title, publication data and more. A "Library" of library data.
Picker: Intermediate and advanced programs have utilities to gather, or "pick", the data you need for citations straight from webpages.
The "Beginner" citation management programs provide quick and easy to use features good for a small handfull of references. Some are simple text entry, some provide automated "lookup" features, and some provide all of the basic citation styles. No program does them all, but they will give you helpful features to get you started. All of these programs work on Windows and Macintosh systems.
In the 2007 revamp of Word, the wizards of Microsoft added a citation manager under the References Tab. Sources are added manually and exported in the chosen style, automatically formatted as in-line citations, works cited or bibliography. This is a great tool for those who have not worked with citations and references in the past and need some guidance.
Started in 2001, this website creates references by ISBN or DOI to create quick MLA citations. It is quick and easy to use with good accuracy. Errors are easily fixed and the overall layout is bright and easy to navigate..
The downsides to the program include: APA and Chicago citations are only available with a subscription; Subscriptions start at $4.99 a month; no in-text citation; advertisements.
Overall a clean, easy-to-use website with ISBN and DOI lookups make this an excellent website for MLA papers.
CiteULike research organizer lives in the cloud (no downloads) and acts as a combo social network (think LinkedIn) and citation manager. You can add resources automatically (sort of - it almost never worked properly during testing) or manually, join like-minded research communities, get suggestions for futher resources based on your added research and set up watch-lists according to your research criteria. You can also tag and rate items and blog about your research.
Note: this free service is supported by ads - lots of them. It also doesn't automatically generate in-line citations or bibliographies.