All my above comments are for animation. For backgrounds I use many different things. Then I use Commotion and AfterEffects to composite them together. Bryce for skies and now trees and shrubs. I use a lot of 2D elements at a distance with photoshop. Commotion allows you to make easy 3D shadows from your 2D object. Nerd has a cool little trick for taking 2D into the 3D world. I use it for short scenes.