Everyone here knows I like to share...just like my friend in school shared these two with me...
This is great because it is easy to use, and it looks damn good for landscape modeling, you can make lakes clouds skies the sun everything and you can modify everything also...the utility is called Terragen and it is totaly free, so check it out...

...another thing is Blender , it is a CG software like maya and 3d studio max but lot easier.

So check them out if you are into this stuff or if you are just curious, for the end take a look at what I made with Terragen in like 2 minutes