Now comes the bump, I chose a combination of a cellular texture and a fractal noise, then reduced the amount from 30 to 14, so the bump is more subtle. You could also scan a real leather texture and use that as a bump if you're so inclined. Another thing to try is adding some more noise, or a bitmap bump / displacement to replicate the wrinkles you get with leather, or model that in as geometry.

Here's a cellular texture, a noise, and then combining the two with a mix.



And here's the final result...



Here's the max file that made the image above, max5: leather_material_max.zip

Here's a maya file for a very similar scene and material, maya5: leather_material_maya.zip