Diana Hacker/Barbara Fister/ Research and Documentation
This is a wonderful online site to help you with research and documentation skills. As a grad student in the MLS program at Hamline, I found this site absolutely invaluable. There is no way you can remember the exact way to document and site each and every type of source from online sites to ancient texts, but Hacker is only a keyboard away from the information you need.
OWL MLA resources
Stephen Wilbers' Weekly Writing Tips
Stephen Wilbers is a writing teacher extraordinaire. For many years, he wrote a weekly writing column in the business section of the Star Tribune. He has the exquisite ability to explain the most useful writing skills in a concise, precise manner. He also embeds a rich sense of humor in his lessons. I recommend his book Keys to Great Writing, and if you would like to borrow it, I have two copies on my book shelf in my room. This link has a new writing tip each week, and they are all useful, and likely to appear on your ACT, AP, and SAT tests in some form.
Stephen Wilbers: Eliminating Wordiness
Wordiness is often the most frequent obstacle to writing well. Think about all the long rambling speeches you have been forced to sit through... Most of the time, the same thing could have been conveyed in half the amount of time.
The Elements of Style by William Strunk
Strunk never goes out of style with people who want to become better writers. His manual is the bible of wordsmiths everywhere.
History of Rhetorical Theory by Ed Lamoureaux
This is an excellent overview of the history of rhetorical theory from the Ancient to Contemporary times.
Grammar Girl: The trendiest grammar guide out there.