The Elements of Style is a style guide for the English language as prescribed by Cornell English Professor William Strunk, Jr. The guide contains rules of usage, principles of composition, commonly misused words and phrases, and suggestions about form. This work, which was later revised and expanded by E.B. White, has been incredibly influential on the teaching of English composition.
Boasting the largest collection of book summaries, BookRags is the best option for titles you can't find elsewhere. They offer all of the basics (quotes, chapter summary, characters, historical context, literary criticism) but also walk through a few major topics that recur throughout the book, which can be particularly useful for essay writing.