Darnit, I missed Naomi's controversial plot idea!
Well, I'd say, something medieval, because mock swordfighting is like the funnest thing ever. I did a movie about a fairy tale in eight grade, and it totally sucked (except for one particularly inspired scene), but we had fun making it. Plus, you can ride horses (rent?), shoot arrows (If you can actually get a bow), wear armor (not real armor of course), and do all sorts of stunts. As for a plot, try a "hero vs. society" type of deal, where the hero is a virtuoso fighter, assassin , or ninga or something and trying to Kill the evil king in revenge because the king killed his father. But, the princess is in love with him, which complicates things immensly. The hero has to have an ally who dies halfway through the movie of course, and the killer is the kings personal guard, and is the real enemy, the one standing inbetween the hero and the king.