A few historical inaccuracies? I saw tons and tons. Without going into lots of politics and so on, a few kinds of statements really jump out. On at least one occasion someone says, "Freedom isn't free" and on numerous occasions they comment on how they are defending reason and freedom from blithering tyrranical hordes. Then there was a mocking of other Greeks as "boy lovers". Maybe I've been exposed to a lot of right wing media but that kind of language is so prevalent in it that you can see how I could come to the conclusion. (I say this without making any value judgments on right wing sentiments, I really don't want to start a flame war, and I realize the potential for it now.)

I haven't read the comic, but I know Frank Miller isn't that political. At least not in his comics. I'm just talking about the movie. Ironically, this kind of language is perfect for Zack Snyder's next movie adaptation of "Watchmen" my absolute favorite graphic novel of all time.

So instead I'll just move on to the tons of historical inaccuracies for the hell of it. I know it was highly fictionalized. This is all just FYI:

Spartan commanders wore the crests on their helmets from side to side, not from back to front like all the other soldiers.

Leonidas DID listen and believe in the Oracle, only the Oracle's prophecy was very different from the movie (though conveniently vague):

O ye men who dwell in the streets of broad Lacedaemon!
Either your glorious town shall be sacked by the children of Perseus,
Or, in exchange, must all through the whole Laconian country
Mourn for the loss of a king, descendant of great Heracles.
He cannot be withstood by the courage of bulls nor of lions,
Strive as they may; he is mighty as Jove; there is naught that shall stay him,
Till he have got for his prey your king, or your glorious city.

King Leonidas and the Greeks weren't stupid, the Spartans used more than 300 men, they mustered their full force which was still drastically outnumbered. The strategy of restricting combat through the pass was going to work though.

The Spartan phalanx never broke unless it was forced to too. In the movie, they did it so things kept moving.

The Spartans used a double edged sword.

The arrows would simply bounce off of the shields. The Persians used cheap bows in large numbers. They never even had a chance of penetrating for the most part.

Spartans individualized their shield designs.

The warriors placed to protect the trail around to the back of the formation weren't slain, they withdrew for fear of Persian retribution. After Spartan scouts reported on the trail's discovery, Leonidas slowly began a phased retreat of his men, until only his personal bodyguard of around about 300 soldiers remained. They stayed behind to keep the Persians occupied while Sparta evacuated. The Persians then razed the empty town. This sacrifice began the idea of a unified Greece, before the Spartans did this, Greece was still something of an abstract concept, so all of the talk about Greece as a high commitment may not be accurate, though I'll have to check.

There are probably a lot more that I've missed.