Good program for 3D modeling? Or just good enough to get ideas out of my head and into tangible space?

I have a lot of stuff running around my brain and I really want to try to get the images on paper so to speak. The only catch is, I'm a terrible artist. Kindergartners laugh at my attempts; my stick figures even seem lacking. So I ask you Answers community, is there a program that can help me develop my skills? I know about Photoshop, but as far as I know, you can't start from scratch with that. My goal is to be able to develop a blank slate into what I'm thinking of.