Download TerraTex – Automated Terrain Texturing/Splatmap Free Unity. 

NEW Lite version is now available for free here

An automated script to texture Unity Terrains based on a wide range of configurable parameters.
Very easy to use, much less complicated than other tools with a user friendly interface and design

Includes customisable layers, with the option to use up to 12 textures for each, and several options for the distribution and blending of these textures.
Customisation options include, though are not limited to: sea level, snow altitude, cliff steepness & texture perlin configuring.