Only set of books that are worth your penny (Especially the fact that it maps all the questions with the OG).

Sentence Correction of Manhattan doesn't even require a review as it is one of the best books available for Indian students for SC.

I think Manhattan GMAT is best GMAT Resources. These are the set of books carefully written with intent of giving the best understanding of given concept. Without any doubt Manhattan SC is best book out there, with that I also want to say about CR Strategy guide also. The 5th edition CR guide is best CR book and it explains the concept at very unit level. Overall I would say great investment for your GMAT perp.

this book is a guide to using your time and abilities effectively. it will work better if you have the gmat official guide, gmat quantitative and verbal review books with you, but only those published by gmac. it explains all aspects and facets deftly and cogently. it will give you inside view on how questions are fabricated and variegated tricks to answer those plethora of questions adroitly and timely. the techniques listed in this book can be used only if possess the patience, aptitude and...

Books are best for quant basics and to score till Q40, but to score above 40 one need more insight.