I found a rather neato Cave and Dungeon Generator, which you can both use for some maptemplates to use in your mods, if you are completely out of level designs
http://www.gozzys.com/article.php?cm_id=11http://www.gozzys.com/article.php?cm_id=8Be warned that both generators won't generate you a picture you can use "out of the box". They will both require some touching up to be used in the game, but it can give you some inspiration. The Cave generator can be used for pretty much any underwater region you are going to do, and the dungeon generator can be used for Cathedral or Sunken City esque dungeons.
The best settings for background and floor in the cave generator are Plain Black for the Walls and either Basic Stone and Sandy, as these are probably the easiest to just white out.
For the Dungeon Generator, the best are obviously Plain Black and Plain White, but it still gives you a grid, walls and doors either way, so that too would need touching up.