Here is a tiny set of terrain tiles with a tool (Blender file) to create more.
These tiles are for continuous terrain, where each vertex can only be 1 unit above/below nearby vertices.
Made per request here
Specs: the tiles are for a base grid size of 64x32. The tiles are 64x48 each, thus each step in elevation is 8 pixels. The first 4 tiles are the same, just rotated.
The shades of those angles aren't based on 3D light, they're self illuminated. Basically the lightest shade is the texture at 100% diffuse intensity, the medium shade is 66%, the dark shade is 33% (I simply made 3 materials with different diffuse intensity but the same texture).
During usage and in specific game engines, you might adjust some tiles up/down 8 pixels; depending on how the engine assumes tiles are vertically aligned.
Usage: Create a texture named "texture.png" and put it in the same folder as the terrain_tool.blend file. Open in Blender and click "Animation". It will create 22 tiles in a folder named "out".
I use this montage script to combine the 22 tiles into 1 sheet:
montage 0*.png -background "transparent" -geometry 64x48 -tile 4x6 terrain.png
(edit) Added two missing terrain options, thanks to Betalord for catching it and testing the results.