Originally Posted by Nick DIY
Google sketchup is free and provides basic functionality for landscape design all in 3-d. Thousands of landscape design elements and tutorials are available free online.
Just an option I wanted to make you aware. I've never personally tried any other design software.
Yes, finally we have a DIYer making an informed, intelligent, and economically sensible recommendation in the Landscaping & Lawn Care forum.
I can appreciate your being excited about having a blank canvas, but I personally wouldn't spend a cent on software. I would ask an old-timer in the landscaping business for ideas, too, as they're happy to give advice and preliminary suggestions / planning for a negligible fee--if not for free.