http://owl.english.purdue.edu/ is one of the best sources I have found. According to the introduction, OWL provides “global support through online reference materials and services.”
Their main divisions are:
*Writing and teaching writing
*Grammar and mechanics
*Style guides which includes formatting and style guides for APA and MLA 2000
The research section tells you how to conduct research (interviewing, surveying, observing and analysis) as well as how to evaluate your sources of information. If you have questions on where to put the quotation marks (inside or outside the period), look for dependent clauses, dangling participles or if a sentence needs a comma, the grammar and writing section can help you.
I have used other university web sites but find I go back to OWL. Instead of reaching for my style books or grammar books, I click on this bookmarked site and find the answers quickly.