Best Sun with ambient color and hard shadows setup ?

I want to try this scene with a sun and also ambient color…

if i use a sunsky in the world tab… i have a nice ambient color… but shadows are difuse …

is there a way to add hard shadows without using a sun lamp ?

You could use a HDR environment map that has a sun in it. If you get one that has good dynamic range, turn on Multiple importance sampling in the world tab - and increase the MIP map size (I used 2048 for the image below) - you’ll get sharp shadows like this:

this is the same scene with MIP turned off

What’s a good manual-page and/or BlenderCookie on this?