for outdoor lighting, usually just a blueish ambient (or gray if it's a cloudy day) plus a bright white directional for the sun (weak if it's cloudy) is all you need, especially if you are using ambient occlusion. Setting the sun light at a lower angle and making the color more orange adds atmosphere. there's a great…
this is a pretty neat tutorial made by zortech over at game-artist.net. Not very lenghty but i found it pretty useful: http://www.game-artist.net/forums/showthread.php?t=413