SketchUp is a fantastic, easy-to-use 3D modelling tool that is brought to you by the folks over at Trimble.  This free-to-download tool is available here, and lets you create, modify and share 3D models.  The Pro version allows you to expand the capabilites with a wide range of plug-ins.

You'll notice on the RS website 3D models are now available free of charge (rswww.com/3d) and are available in .skp format - SketchUp compliant.  

Manufacturer

Trimble

Website

http://www.sketchup.com/intl/en/index.html