I have been playing with Metacreation's awesome 3D Landscape Software, Bryce 3D, for a while now.  These are just a few of my latest ones. Metacreations sold the rights to this program to Corel. UPDATE - I have been using Bryce 5 for almost 6 months now, and it is a big improvement over 3D! Pictures to follow...  I recommend that if you are interested, you try out Bryce 3D or Bryce 4 or 5. Up until recently it was possible to download a demo for Bryce 5 from the Corel website, but for some reason it has now disappeared.... I still like Bryce, even though many of the pros have moved on to other programs.   They do have some interesting capabilities.  I first found out about this program from a website called "DigitalBlasphemy.com".  The work he does is awesome!!!  To quote from Heinlein, "I am an egg"...  I have also done a little bit with TerraGen, another landscape rendering engine, and have been playing with PhotoShop 7 for post-rendering as well.  Here is a sampling of some of my favorites...
  
Hubble Dawn
(TerraGen + PhotoShop + a really cool picture from the Hubble Telescope)
Moonsrise
(Bryce 3D)
Oasis
(Bryce 3D)
Oasis II
(Bryce 3D + PhotoShop)
Partners
(PhotoShop 5.0 + Photo by Jennifer Gerber)
Wingshooter
(PhotoShop 5.0 + Photo by Jennifer Gerber)
Europa_Resort_thm.bmp (518454 bytes)
Europa Resort
(Bryce 3D)
FrannasCastle_thm.bmp (518454 bytes)
Franna's Castle
(Bryce 3D)
gaiatemple_blu_thm.bmp (518454 bytes)
Gaia Temple
(Bryce 3D)
lonetree_thm.bmp (518454 bytes)
The Last Christmas Tree
(Bryce 3D)
mayantemple3_thm.bmp (518454 bytes)
Mayan Temple
(Bryce 3D)
SnowMtns_thm.bmp (518454 bytes)
Snowy Mountains
(Bryce 3D)
serenelake_thm.bmp (518454 bytes)
Serene Lake
(Bryce 3D)
Columbia_thm.bmp (518454 bytes)
Across the Columbia
(Bryce 3D)