This is the first post on the parsha I've made from the library - which means no time for extensive saving, revising, and editing - which probably means it's less thorough than usual, but also less boring.
Steg suggests that Pharoah's phrase "look, ra'ah is opposite you" (10:10) refers not to generic evil, but to the Egyptian sun-god, Ra.
What makes this theory especially interesting is the verse's context. Moshe has just announced the 8th plague: "Behold, tomorrow I will bring locusts in your territory. They will cover ein haaretz, and it will be impossible to see the land..." (10:4-5). Onkelus translates "ein haaretz" as "ein shimsha de'ara" - the "eye" of the sun which shines on the land. Apparently, Moshe is announcing that the locust horde will be so thick it will totally block out the sun.
If so, then Pharoah's mention of the sun-god at this moment is especially apt. "You think your plague can block out the sun? Impossible! Ra will never permit that! Maybe YKVK can take on our lesser gods, but he better not try to mess with our chief god, the sun god!"
Of course, the locust plague takes place as Moshe predicted, and the Torah specifically mentions that the land grew dark during it. Not only that, but the next plague - darkness - seems to be solely directed at the purported sun god. And the final plague occurred at midnight. In fact, the final three plagues all took place in darkness.
This seems like a clear and conclusive lesson to the Egyptians and Israelites that the sun, or a sun god, are not to be relied upon.
UPDATE: Here is more support for my thesis. Or, my post is more support for his thesis. Or something.