Many databases, such as Gale Virtual Reference Library and UW Libraries Search, offer a tool that will automatically generate citations in MLA/APA style you can copy/paste into your Works Cited sheet.
You can also plug the title or author of most articles/books into Google Scholar (http://scholar.google.com) and get the citation:
If you use a citation generator, do remember to check the citations for errors using one of the resources in the box below.