My favorite is the well-known program of Bryce. It is easy to use-and has a wide range of capabilities. However, it is not terribly good for modeling ships-but I have made some impressive ship designs with it.
Infini-D is the program that made the original EV ships. It is slightly similar to Bryce-but rather old. It might be freeware, but I realy don't know.
Mechanisto is another thingy that has been used by many plug-in developers. I barely know anything about it, but I know it does have downloadable demos.
Carrara is an almost unheard-of program. Probably because it's brand-new. I do have it though, and it is ONE OF THE BEST PROGRAMS OUT THERE! It's like all the above combined, and with the capabilities of Ray Dream Studio. It's got a spline-modeler, vertex-modeler, and METABALL modelling.
Let me give you some advice: if any program has a metaball modeler, it's got Media Grade qualities (it can be used in commercials and the like).
It also has a new feature called 'Physics'. This lets you apply the laws of physics to any object like a preset! You can make fallen leaves sweep up from a gust of wind, or make a ball bounc on the ground automatically!
Carrara is not necessary for EV ship designing though. I suggest Infini-D and/or Bryce.
(You would get more replies if you post on the developer's board!)