ProgressiveDreamer,
I wish it were that easy!

I don't have a full list of all the rules, but here is a list of the most tested concepts:
-Subject-Verb Agreement
-Verb Tense, Voice (present, past, past perfect tenses, passive vs. active voice)
-Pronouns (agreement, ambiguity, subject, object pronouns)
-Modifiers (noun modifiers and adverbial modifiers)
-Parallelism
-Comparisons (like vs. as vs. such as)
-Idioms (we have a lengthy list in the
Manhattan GMAT guides, and I'm sure there are other lists floating around the forums)
-Connecting Punctuation (semi-colons vs. commas)
Hopefully this helps!
Brett