I took a look at TerraRay recently, and found it a good, low priced 3D scenery generator. It didn't have the features of the big boys like Vue or Bryce, but it is a fraction of the price. One of my biggest complaints in my review was that the rendering was slow.
Now the app has a free update to version 5 for current users, and a 50% off price of US $9.99 until September 26. You can find TerraRay at the Mac app store.
In my tests, rendering speed has increased about 3x over version 4.5. The app has also added a configurable preview window, support for Lion full screen mode, some built-in sample scenes to get you started and that you can modify, as well as improvements in texturing.
One thing I'd like to see is more control of the position of the sun. You can't easily change the sun elevation. Instead, you have to drag the sun's position around a bit to fiddle it into the place you want. I'd like to see the ability to just add numeric input for azimuth and elevation.
On the whole, this app is a solid, entry level renderer. If you're not ready to spend hundreds of dollars for high end landscape creation, TerraRay is competent and now a lot faster. You can check out a video of the app here, and take a look at some screen shots from my sessions in the gallery below.