You can find a few ideas here :
http://trackertrail.com/index.html
And if you can get hold of the Rockies episode of Extreme Survival, Ray Mears shows an interesting shelter for forests: a raised bed made of young truncs (young because they are thinner and lighter) for insulation from the ground, with a good layer of pine branches for further insulation and comfort, then he build a lean-to of the same type of truncs (not much more than 10cm diametre if I can remember right), and covered it with a layer of moss then pine branches for waterproofness. It had to be quite steep for the rain to run down. He then did a fire as long as the bed in front of it, and said that with that setup he could sleep down to -50° (if I can remember right, and I don't know if it's Farenheit or Celsius)
In the "Alps" episode, he also shows how to build a snow shelter, he did it with a normal woodworking saw (the type with a thin, long and high blade, if that makes any sense) to cut out the blocks, it looked much faster than cutting out the blocks with shovels as I do when I build igloos with my friends, I'll try it this winter

Anyway, he built it with a "ditch" between the two beds, so that the cold air goes down and doesn't cool the beds down...(snow beds of course)
Seems the debris hut is also quite popular.
Hope that helps a bit.