That’s the first one that came to my mind too. You can also say more shortly εἰς κόρακας. I think it’s the Greek equivalent of “To Hell with you!”. The point is that for Greeks, burying a dead person’s corpse was very important. With this curse, you’re hoping that the person’s unburied corpse should be eaten by crows.
Generally, Aristophanes is a good source of Greek curses, especially the really obscene ones.
The Greeks tended to swear by their gods. E.g. μὰ τὸν Δία “By Zeus!” (I think this is mostly used in a negative sentence, in an affirmative one I guess you’d say ναὶ (μὰ) τὸν Δία). In the Apology of Socrates, Plato uses a very mild expletitive μὰ τὸν κύνα, “By the dog!”, to avoid naming an actual deity. I think this is very mild like “Gosh!” or something.
I think the god by which you swore depended on who you were. In different places different deities were more important than others and were more likely to sworn by. Also, I think women were more likely than men to swear by female deities. I guess also your profession and age had an effect. I’d hazard also that the situation that made you swear had an effect on the god you swore by. (I guess you didn’t swear by Demeter if a storm broke out in the sea, and you didn’t swear by Poseidon when you discovered that all your figs had been eaten by ants).
Greek cursing is actually a subject I’d like to know more about myself. I haven’t really read any good treatment on the subject, just a bit here and there, especially while reading Aristophanes. Perhaps there’s someone on the forum who can teach us something?