Attached Link: http://www.rhino3d.com

Well, not to take away from Trav's post... I use Rhinoceros3D to model. It's one of the most powerful, easy to use nurbs modelers available. I try to use sketches as reference when I can but sometimes I just jump right in and model. My modeling method of choice is Lofting and then point editing (sort of like vertex editing but simpler and far more powerful). I hope this answers your questions.