3D tools:

• GroundWiz by Gugila: procedural texturing.
• DreamScape by AfterWorks (Sitni Sati): Seascapes, skies, clouds and more.
• 3D Studio Max by Autodesk

Links relating to procedural geometry:

• Generating complex procedural terrains using the GPU
• Nvidia's Cascades demo
• Implicit surfaces voxelization
• Isosurface tutorial
• Procedural planet