BTW of the stuff I recommended, I can highly recommend Augustine's Confessions, Caesar's Conquest of the Gauls, and Livy's History of Rome.... I've read all of the Confessions, about 80% of Caesar, and only about 1/3 of Livy, but they were all very good and pretty engrossing/exciting/fun-to-read/whatever. And now they're sitting on my shelf waiting for me to pick them back up after putting them aside after I had read all I needed to for class
Plutarch is supposedly one of the greatest prose writers who ever lived... I own the Lives, but I haven't really started to read them yet, so I can't confirm how good they are. It sounds like a pretty interesting idea.... he goes through Roman and Greek history, picking out pairs of famous men (one Greek and one Roman), writing a biography of each, and then a third section comparing the lives of the two men.... he picked them out so that there would be interesting things to compare/contrast (e.g. two generals, two tyrants, etc.). I forget how many there are, but there's quite a few....
linky The Lives are actually where we get a lot of our knowledge of ancient history (esp. Greek) because he got his information from a lot of other works that have subsequently been lost.

I used part of one of the Lives (Agesilaos, one of the kings of Sparta) for a paper I wrote on Sparta. Spartan history is particularly... well, Spartan

so most of the modern scholarship I found on Sparta referred heavily to this one biography, plus a small section in Aristotle's Politics and a few things from Xenophon.
As for Aristotle, I've read most of Politics and Nicomachean Ethics, and all of Poetics.... I own the Metaphysics and Posterior Analytics (supposedly these two go together) (well, really, all of Aristotle's stuff goes together, but these two in particular... Nic. Ethics and Politics are the same way) but I haven't started to read them yet. I really like Aristotle... he's a ton better than Plato IMO. I could hardly stand the Republic. Bleahhhh Plato
If you want to move to the foundations of 'modern political thought', I can recommend Hobbes' Leviathan and Locke's Two Treatises on Government (sorry, I forgot exactly which treatises, but they were in one volume when I used them for a course my first year.).