Google Sketchup 8 (free)
It never ceases to amaze me that Google Sketchup (now on version 8) is a completely free tool. For those who have not heard of it, Sketchup is software that allows you to create 3-dimensional designs. What I like most about it is that its extremely accessible to novice users but is sophisticated enough to do some very impressive modeling.
This year, I'll be working with 7th grade math students who have been asked to come up with new designs for water bottles that use minimal material but hold a lot of volume (they are studying 3D geometry). They will use Sketchup to create several mockup designs, and then will create a physical prototype using the design they are most satisfied with.
Last year, I used Sketchup to create a model of a renovated technology center in my school, starting with nothing but the floor plan provided by the architect leading the redesign.
Kerkythea (Freeware/Open Source)
I found Kerkythea earlier this week when exploring different plug-ins for Sketchup. Kerkythea is a standalone image renderer that has a tool in Skethcup that allows you to add lighting points (sun light, lighting fixtures, etc.) to create pretty amazing renderings of the relatively plain looking Sketchup drawings. It has a bit of a learning curve, but there are some decent tutorials out there. I don't really quite know what I am doing when I use the program at this point, yet I was able to make a pretty awesome version of the photo above in a matter of minutes while following a tutorial from the Kerkythea website.
Header photo by Robert S. Donovan