I know Blender is a very good and FREE 3D modeler, I don't know if it's easy to model cars with. But maybe you should check it out, there are also a lot of tutorials about blender.

http://www.blender.org

Good luck

It's nice to see how well you can model with sketchup. I still have a lot to learn and love to watch this topic.

I see you were looking for blueprints. I know a lot of people use this website for there blueprints, I hope it can help you (and all the others on this forum): http://www.suurland.com/

-Denman