Material Maker - Cross-platform, procedural texture generation tool.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Filter Forge - On the surface, Filter Forge is just a Photoshop plugin, a pack of filters that generate textures...
Autodesk 3DS Max - 3ds Max is software for 3D modeling, animation, rendering, and visualization. Create stunning game enrivonments, design visualizations, and virtual reality experiences.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
ZBrush - ZBrush is a digital sculpting and painting software solution.