Looking for a great program for 3d modelling? You should check at this site
http://www.planit3d.com/source/software_files/3dmod.htm. I think Truespace 3 is one of the best programs on the site. You can also get photo-realistic terrain generation software
http://www.planit3d.com/source/software_files/terrain.htm, which is great for making skyboxes. And it's all free!