Unwrapping
This technique is great for applying accurate detailing to a complex shape. All the facets of the model are unwrapped and laid flat as a bitmap image ready for work in your favourite photo software. There are various unwrapping programs available as both stand-alone programs and plug-ins for the more popular 3D apps. A quick search on the net should turn up a few or visit Ultimate 3D Links at  http://www.3DLinks.com
The texture map below for the statues head was created by first hand brushing some shading/weathering around the eyes nose etc just in greyscale on a transparent

overlay using the unwrapped image as a guide. Next the carvings were drawn dark grey on light grey overlay and reverse embossed to appear carved. Now the two overlays were brought together as one greyscale overlay, multiply merge mode for the shading layer over normal mode for the carving layer . For the overall stone I used an Artshop limestone texture to which the greyscale overlay was added with the merge mode set to Hard Light, the opacity reduced to suit.
Finally the finished image is applied to the model using spherical mapping

Top Left, the unwrapped head. Below Left, completed artwork. Above and below, the texture applied to the model.