Google Sketchup or FormZ...my preference.

I'm asked quite often, "what program should I use for 3 dimensional design"?

This comes mainly from other art directors, production designers,  set designers, or illustrators.  Originally, I would have suggested Sketchup because of it's ease of use and interface. In fact, I've been a user of Sketchup for several years (back to Version 3.0)! Also, I used Alias' program "Sketch Up" (which has long now gone away) to generate blocking models for set design and illustration.

I'm glad to now suggest FormZ jr (formerly bonzai3d) from Autodessys. I've used their program, FormZ for many years, and I'm excited that they have produced other variations of FormZ. It's very simple to use, quite similar to Google Sketchup, yet provides more modeling versatility and what I find an easier environment to design in.  One of the features I like is the ability to have multiple viewports open at once (top, side views, and perspective), and the ability to render with additional lighting directly in the program.

Pricing  for FormZ jr (without the rendering plug in) is the same as Sketchup Pro. Another advantage of the pricing for FormZ is the license is cross platform, so you'lll be able to use it on a Mac OSX or Windows platform.