You could do worse than actually read Book 7 of Herodotus if you're interested in primary sources.
Stephen Pressfield also wrote a relatively popular "historical fiction" book on this same topic called, I believe, the Gates of Fire.
Trailer looks pretty good.
I'm more an ancient history geek than a comic geek, but I'm looking forward to this. But I don't get to go to the movies any more...
Mr Mephisto