Grammar Girl Grammar Girl can help with grammar and writing questions.
LitCharts LitCharts has many study guides for novels. Beware: the study guides should not be used as a substitution for reading the novel!
The Elements of Style "Asserting that one must first know the rules to break them, this classic reference book is a must-have for any student and conscientious writer."
Literary Devices Website is easy to use and contains an extensive list.