in the post that has a list of all mods appear these mods for extra ships/skins (that you can use to invent more ships if you know how)
http://www.subsim.com/phpBB/viewtopic.php?t=41256
http://www.subsim.com/phpBB/viewtopic.php?t=39396
also, there are a lot of mods, skins and stuff here:
http://u-boot.realsimulation.com/
i hope this helps