Pre: GeoControl 2. The erosion routines rule and I like the sculpting-like control over my terrain, especially like the water-flow management.
TG: For now I'm using TG to generate my skies and far-away terrain and export as sky-boxes.
Post: Export skies and terrain/bitmaps into Blender. Not really happy with converting the great TG procedurals to a dumb-ass mesh, but don't know what else to do. I need Blender for the full suite of modeling/animation/FX tools.