I don't particularly have anything in mind but why not have a few things to show off your range? Do some general movie quotes that show off various emotions or personality traits (anger, interest in what the other character is saying, light-heartedness, sarcasm, humor, etc.).
Another thing that would be helpful - and is often overlooked by voice actors here - is to show off your narration skills. Do a monologue from a play you grab from your web or your local library! (If you can't think of any to do, I suppose you could always try narrating one of the Star Wars scrolls, either from the movie or one of the games.