This site starts with the basics--what is a noun, what is a verb, etc.--and quickly ascends through all the major building blocks of good sentence structure. Here are the sections I specifically recommend for GMAT prep:
- The Parts of the Sentence (complete lesson)
- Using Pronouns (Pronoun Reference)
- Using Verbs
- Compound Verbs
- Auxiliary Verbs
- Linking Verbs
- Verbals
- Forming and Using Verb Tenses
- Using Verb Tenses
- Using Verb Tenses in Sequence
- Using Verb Moods
- Modifiers (Misplaced and Dangling Modifiers)
- Building Phrases (complete lesson)
- Building Clauses (complete lesson)
- Building Sentences (complete lesson)
- Miscellaneous Topics
- Apposition
- Noun and Pronoun Characteristics
I know that's almost everything they have, but what can I say--grammar is a huge subject! This information is the perfect background to complement Veritas' VAMPIRES methodology for Sentence Correction questions, and can be an invaluable aid in your AWA and application essay writing as well.
One caveat that I should mention: HyperGrammar is Canadian, eh? That means that the Queen's English sneaks in from time to time. They use standard OED spelling (read: British), but don't let that throw you! The materials covered all look good and test-ready to me--even the discussion of the subjunctive mood, whose usage in British English differs slightly from formal American English (the dialect of the GMAT).
http://www.uottawa.ca/
