This is a map I made for Hydra Team DeathMatch. Check out Hydra here: hydra-minecraft.net/index.php?page=main
The idea is two ships fighting each other, with Red team being the Pirates and Blue team being the Navy. I know that that's a little prescriptive, but what's wrong with a bit of background?

There are Splash Potion of Healing spawners at the team spawn points, which allows quick healing even for classes that do not normally have healing. There are two levels to the ships, the lower of which has holes in the side to allow archers to fire at enemies that are swimming across without getting hit themselves (if they stay behind cover). There are also masts from which archer classes can rain arrows on the enemies below, but it is quite hard to hit anything from that height, and the clouds might obstruct your view.
This was made with MCEdit.