Many different colleges and universities provide online access to their helpful writing and grammar guides. Here are a few:
Online Writing Lab (OWL)
Use this as an online citation manual for APA, Chicago, and MLA.
Harvard Writing Center
Useful writing guide for a variety of issues.
This site, created by the Capital Community College Foundation, provides easy drop-down menus that can help organize a paper or check for correct grammar use.
More Grammar Sources
Further resources on grammar and style from the University of Chicago’s Writing Program.
Elements of Style
The classic reference book by William Strunk, Jr. will help correct many common mistakes.