Sketchup - free 3D tool by Google
Many of you might not be knowing that there is a free tool named sketchup, released by Google that can help you in creating viewing and modifying all types of 3d designs.
There are 2 versions available, one is free version and another is pro version and it costs $495 which is pretty much just like other 3d design programs.
You can use sketchup to create 3d models of houses, gardens, buildings or any other of your imaginations.
You can also export your files to Google earth, which is really a very great feature.
There are lot of pre drawned components also in its inbuilt libraray which you can use while creating models for your house 
Its available both for Mac as well as Windows.
Requiremnents for Windows based PC are:
Current sketchup version: 5.0.295
* Microsoft Windows® 2000, XP Home or Professional Editions
* 600 MHz Pentium® III processor
* 128 MB RAM
* 80 MB of available hard-disk space
* Video card that is 100% OpenGL compliant
* Windows compatible pointing device
* Microsoft® Internet Explorer 6.0 or higher
* Windows® Media Player or QuickTime 5.0 and web browser for multimedia tutorial.
Requirements for Mac based PC :
Current sketchup version: 5.0.296
* Mac OS X®
* 400 MHz PowerPC™ G4
* 128 MB RAM
* 80 MB of available hard-disk space
* QuickTime 5.0 and web browser for multimedia tutorials
* Video card that is 100% OpenGL compliant