Sweet Home 3D

This is an excellent software package for laying out room designs and then visualizing them.  Best of all, it is high-quality, free software that works on Macs, PCs, and even Linux.  Definitely worth checking out:

http://sourceforge.net/community/potm-200910/

Tom and I have been using this software for the last few months, and while it requires a bit of an engineer's mentality to take accurate measurements and adjust the furniture models to your exact dimensions, the end results can be quite realistic.

And it also prints out nice blueprint style documents:

Note that the Concept sketch a few posts earlier was done by our general contractor, who wanted to learn Google Sketchup.  Also a fine product, it emphasizes a different but also interesting visual style.