Game Terrain Design

What would be the best program to use if I wanted to design Game Terrains on the PC?

read the topic "First Completly Digital Animation".

Terragen is a great program, but if you're going to be doing game design, you'll need to export the terrain to a format that the game engine can understand, and if I remember correctly, terragen won't export at all.

Also, the OP didn't mention whether he was wanting 2D or 3D terrain, What kind of game it was going to be, or what game engine he was planning to use (if it's going to be a 3D game)

I know many are quite keen on POV-Ray for 3D graphics. You can see some examples of what people have done with it from a recent competition . JPatch is a java based 3D modeling tool that can be used with POV-Ray. If you'd like to get a really good feel for how extensive it's capabilities are, click the Imposter movie and watch that. It'll blow you away.

Of course, I'm sure those people didn't just develop those skills over night either. Gonna take some significant work to get that good.