I have the Greek Reader app loaded on my iPod Touch. It doesn't actually have the Greek NT text but instead will list the "rarer" words that occur in the text (you set the minimum number of occurrences, presumably according to your reading proficiency level).
I'm not sure I would "recommend" it as I was hoping when I downloaded it that it would have the actual Greek text, which it does not. Plus it wasn't free. But you might find it useful.