Blender has been developed by a community of open source programmers and so is available for free, using it you can create professional looking 3D models, it is a program where the sky really is the limit.
If you are new to 3D you might want to explore using Google SketchUp first, as Blender is quite an advanced tool with a complex interface.
To download your copy of Blender click here.
Blender Nation is an interesting website that features all kinds of things to do with Blender, from tutorials to examples of work.
Video tutorial from YouTube.
If you are feeling brave, why not install Blender, watch this video and have a go at teaching yourself?