Reddit mentions of Aristotle's Physics: A Guided Study (Masterworks of Discovery)

I don't know what Kenny means there. A bunch of stuff in Aristotle's scientific works is super relevant to understanding his general ontological outlook (i.e. his concept of substance), which is still philosophically relevant, since there's a contemporary resurgence in neo-Aristotlean metaphysics.

If you want to read the Physics, and if you don't have much background in Aristotle, I really recommend Joe Sachs' edition. He's able to make a lot of the key ideas super clear. His IEP entry on Aristotle's view of motion is a great overview of some of these ideas, and is worth reading as a starter to see if you want to delve into this stuff more deeply.

If you're interested in the Aristotle's way of thinking about things (natural and otherwise) more broadly, I can't reccomend Aryeh Kosman's The Activity of Being highly enough. It's at once an accessible and rigorous introduction to Aristotle's theoretical thought.

Here is his translation of the Physics on Amazon:
http://www.amazon.com/Aristotles-Physics-Guided-Masterworks-Discovery/dp/0813521920/ref=sr_1_2?ie=UTF8&qid=1346385001&sr=8-2&keywords=physics+aristotle

I'm sure you were looking for PDFs or something, unfortunately I don't know of any links to those :\ I'd love a link if you actually found any!

He also wrote these articles online:
http://www.iep.utm.edu/aris-poe/
http://www.iep.utm.edu/aris-met/
http://www.iep.utm.edu/aris-eth/
http://www.iep.utm.edu/aris-mot/

But yeah, after reading Aristotle's Physics, I've come to a basic conclusion that his entire philosophical system emerged out of a refutation of Zeno's paradoxes—he spends the second half of the Physics destroying those arguments as well as big chunks of the Metaphysics (or so I hear). What's crazy is that most philosophy students (even graduate students!) only read the first half of the Physics! The first half is only his introduction to the refutation of Zeno in the second part (oh, by parts I mean the chapters before and those after the three middle, or 'topical' chapters, i.e. Time, Infinity, and one more that I can't remember right now—oh! two more: space and place). So yeah, I'd start with the last of the articles I posted up there (on Motion) and then go onto Metaphysics.

Hope that helps! :)

If you want the Johnnie perspective on that, I'd recommend reading Harvey Flaumenhaft's introductions to the Masterworks of Discovery books. You can read it online on Amazon with the Look Inside feature.

I, for one, find that reading math / science works in the original is interesting beyond the history, challenging and educational. YMMV.

Sorry to bother you, but what field is that? Ancient Greek mathematics, or their physics?

To OP:

A little late I know, but I'd also have to recommend Galileo's Two New Sciences. Galileo requires a knowledge of parts of Aristotle's Physics, which I'd suggest anyway if you're interested in this. A quick note on that translation, Sachs is a very difficult but very rewarding translator, in my opinion. He focuses very closely on the Greek at the expense of using rather confusing language at times. If that's not what you're looking for, the standard translation (including standard vocabulary) is contained in this collection of Aristotle's works. Archimedes, as others have suggested, is great. Heath, the editor of that volume, is a fantastic scholar and his 3 volume edition of the Elements for anyone looking for an in depth knowledge of Greek geometry. Heath's two volume history of Greek mathematics is a must have as well for that subject. Newton is another very rewarding author (though the Principia is very challenging). You'd probably be looking for the Densmore edition of the Principia, which makes the Principia extremely more accessible.