Tectonics
http://forums.civfanatics.com/showthread.php?t=149278

Tectonics does a very good job at creating semi-realistic land masses with interesting terrain and choke points. I recommend using either "Earthlike (70% water)" or "60% Water" settings to get a nice collection of continents with a few small islands spread around.

For a naval-centric setup, try "Islands", which creates a lot of smaller islands and probably close to 90% ocean.