Using the MCedit filter that allows you to edit mobs, and make them into spawners, and then into spawner-carrying minecarts I made this ship. The spawners it carriers and drops spawn invincible, jump boosted, water breathing, charged creepers. Yeah. Just push the spawners out of the cargo hold, and if they land somewhere dark they pump out the monsters that attack anyone unfortunate enough to be in the area. The logic behind it being that if you can just selectively destroy an area's population, why flatten the entire city/fort/ship? It's also scary. The ship is crewed by four people, has five dispensers for self defense, and has 4 bunks, a cockpit, a small galley, and a very small recreation alcove. Pretty humble.
Needless to say, the ship is lit up like a chandelier, inside and out. Just one of the green chaps could ruin the crews day (Read: Kill them all and cause the ship to crash) Luckily, that same explosion would probably destroy the other spawners.

Warning: May cause lag. I would not suggest you drop all the spawners in one area.

Holy $&!#!! With multiple spawners this brings me down to about 5 FPS! I say you take off and nuke the entire site from orbit, its the only way to be sure. (read: delete it from your world or destroy some spawners.) But the again my computer sucks.

Creative idea? Please, I would like feedback.