This may be another one of those that falls into the category of "everyone knows this but me"...but...

I found this nifty trick for precise placement of the sun or moon in an image:

1. Switch into the "sky and fog" menu and hold down ctl+alt and double click on the sky sphere.
2. For the sun hold down ctl+alt and click in your scene.
   For the moon hold down ctl+alt+shift and click in your scene.
3. The position is shown by the asterisk, (it will be blue for the moon and yellow for the sun)

cool huh?