UPDATE! The MLA has totally revamped their citation style (as of Spring 2016); until I get it figured out, my courses will roll with the 2009 edition.
The citation bible for undergraduate English majors is the MLA Handbook for Writers of Research Papers, 7th ed. (2009). It's fairly inexpensive, and you can probably find used copies more cheaply. If you're a card-carrying English major this ought to be on your shelf. It is certainly on the shelves and behind the reference desk at Main Library, and is the ultimate arbiter in citation format. There are also lots of 'pocket' guides out there. I can't speak to these, but if you use one be sure it contains the 2009/7th edition updates. (Earlier editions will not give you the most up-to-date information for online sources, so don't be tempted by their minimal price tags.)
For quick and universal access, I strongly recommend the synopsis of MLA format provided by the OWL at Purdue University. Please refer to it for both paper formatting guidelines and citation styles (in-text and Works Cited). This site should cover all your needs, except for very arcane print material or tricky websites, about which you should be asking me anyway.
The Cornell University Library also provides a useful breakdown of the most common citation needs.
Beware of citation generator software! There are many out there. Some have historically been quite accurate, and some have been notoriously wrong. So, as with any digital gadget, be a savvy user (i.e., don't use the el cheapo online ones) and don't assume that the citation generator will get everything right. Check your Works Cited page before handing it in -- you, not the citation generator, are responsible for its accuracy.