First thing with terragen.

Here.

Any comments? Terrain,water, and clouds rended in terragen. I did all the post-processing in photoshop.

Well...The objects in the picture look like they are floating. They have a sort of glow around them, and its not convincing if your going for "real" look. What I would do is work the edges of what you have there, adjust the levels and contrast til everything looks realistic in tone and texture, and especially smooth out the cloud edges.

Looks very...terragen.

It's not bad, but it looks very canned. So do most other terragen images.

You may want to experiment with some other rendering programs in order to get a more realistic effect. Unfortunately, I don't know any.