First there was the free on-line room planner, and now, just in time for planting season, we have the free on-line garden planner. You draw your dream garden and then pave it, plant it, and populate it with such things as trees, flowers, ponds, fountains and even garden gnomes. The website should come with a warning, however: "Users may become addicted." Oh, but what fun!
Note: the free version does not support saving files, but you can print them. And, of course, there's always 'print screen'.