Most 3D modelling apps can import vector graphics and create 3D models from them.
If you are adept in vector graphics you might like a NURBS modeller, NURBS are the 3D equivalent to 2D vector graphics. Try the demo of Rhino 3D, you can save 25 times with it. Also you can head over to the Rhino forum, they have some very good tutorials there.

There are some other good free or cheap 3D modelling programs out there, I'm sure someone else will provide some links. :)