Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Material Maker - Cross-platform, procedural texture generation tool.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
ZBrush - ZBrush is a digital sculpting and painting software solution.
Filter Forge - On the surface, Filter Forge is just a Photoshop plugin, a pack of filters that generate textures...