Material Maker - Cross-platform, procedural texture generation tool.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
TextureLab - Free, Cross-Platform, GPU-Accelerated Procedural Texture Generator.
Cinema 4D - Cinema 4D is a 3D modeling, animation, motion graphics and rendering application.
Filter Forge - On the surface, Filter Forge is just a Photoshop plugin, a pack of filters that generate textures...
Autodesk Maya - Maya is 3D computer animation software with powerful modeling, rendering, simulation, texturing, and animation tools for artists, modelers, and animators.