Try 'split' designs. Most designs tend to focus on a single (usually spherical) hull shape, with engines and weapons bolted onto the sides. Including mine, now i think of it.
Also, cockpits which are set quite far back, or even which do not exist - i.e. the pilot uses cameras & a special hud. Or, ships built more on a vertical axis - b-wing is the best example, I guess.
Or go nuts and make the ship as being a single unified block - i.e. barely a cube - and use up the polys adding the fine detail.
Design inspiration..... I'd say look at natural shapes (very roughly), machinery as bob said, um.... well, not sure. Maybe more esoteric stuff like gargoyles & gothic art. another way is to actually think of movie-like sequences, very roughly. I.e. an attack run on some big ship - if you spend enough time, then your subconcious should pick up the effort and start 'adding' details that'll just pop into your head.
Trick then, is to have somewhere handy to jot it down.