Which edition of Philosophiae Naturalis Principia Mathematica of Isaac Newton would you recommend to me? I'm searching for a good edition of Philosophiae Naturalis Principia Mathematica of Isaac Newton in English. Which edition of the Principia can you suggest me? If it's possible, cheap and similar to original with the original proofs of Isaac Newton.
I'm sorry for my poor English, I'm just learning it.
 A: Here is a free copy offered by its author, (edit: the translator, Ian Bruce),


*

*http://www.17centurymaths.com/contents/newtoncontents.html
A: This 2003 edition by Densmore & Donahue has the following book review

Makes the great adventure of Principia available not only to modern
  scholars of history of science, but also to nonspecialist
  undergraduate students of humanities. It moves carefully from Newton's
  definitions and axioms through the essential propositions, as Newton
  himself identified them, to the establishment of universal gravitation
  and elliptical orbits. The guidebook unfolds what is implicit in
  Newton's words as he himself would have filled in the steps and
  completes the argument in ways that are authentic and not
  anachronistic, exactly following Newton's thinking rather than
  substituting tools of modern calculus or the formulations of modern
  physics. It is Newton in his own terms. This is a wonderful book.
  ―Richard S. Westfall

A: The difficulty is not in the language that Newton uses, but in the incredibly original viewpoint that he takes.  Get a good translation, by all means, but you'll also need the help of a good guide.
One of the best such guides I ever found was S. Chandrasekhar's fantastic "Newton's Principia for the Common Reader", Oxford University Press, 1995. (Don't be fooled by the title, though, apparently Chandrasekhar had a much higher opinion of the 'common reader' than is warranted by the available evidence.)
It doesn't cover the entire Principia, but mainly the parts that lead to Newton's results on gravity.  What Chandrasekhar does is explain Newton's propositions, translate them into modern notation/language and show you a 'modern' proof, and then, with that knowledge of what is going on, he goes back to Newton's argument and shows the reader how Newton's approach works.  Along the way, he comments on how Newton's ideas harked back to Euclid and, at the same time, anticipated concepts in mechanics that would not be developed until many years later.  
It's an amazing, edifying work by one of the greatest astrophysicists of the 20th century.
A: I would recommend this 1999 version by Cohen & Whitman:
The Principia: The Authoritative Translation and Guide: Mathematical Principles of Natural Philosophy
This edition has comments that help you understand the original. It is also quite cheap.
