As far as hard surface modeling goes, automobile models are probably one of the most commonly seen examples (you didn’t think all those perfect images in auto advertisements were the real thing did you?) There’s a huge industry out there that could use the skills of talented ZBrush users like you! If a career in modeling or perhaps even designing automobiles is something you are interested in, ZBrush Central member Withamin has provided a great place for you to start, even if cars aren’t your thing but you have an interest in hard surface modeling with ZBrush in general. Have a look at his easy to follow tutorial he has been kind enough to post to ZBC that will get you moving in the right direction in no time.
Hard surface modeling tutorial for automobiles at ZBrushCentral.com