Hi guys,
as many people said, keyboard and mouse are nice to play ship simulator.
in my opinion, no wheel can fit the need of ship simulator, as the wheels you have onboard ships don't react like those you have on a car (they don't reset to neutral when you release them).
As Capetan Thanasis said, the most enjoyable is a double lever controller for two-engine ships. And for this, I can recommend you this hardware, made by saitek (initially made for flight simulation, but works perfectly well with ship sim too) :
http://www.saitek.com/uk/prod/quad.htm
regards,
Denis