Super and a very cool resource on tenses called The Tense Tutorial
by Aristotle Prep (guys who make the SC and CR Grails) . Provides great clarification with detailed, pictorial examples of each type of tenses. Must read I say! You can download the ebook from below.
P.S. : I have sought permission from Aristotle Prep to post the ebook here.
GMAT Demystified: gmat-demystified-great-ebook-to-get-started-with-download-140836.html
Tense Tutorial: uber-awesome-resource-on-tenses-download-140837.html
CR Question Bank (LSAT): critical-reasoning-question-bank-download-140838.html