PS - selection, layers

Selection Tools Tutorial

Selections Tutorial

Making Selections

Layers Tutorial

http://www.uwec.edu/help/PhotoshopCS2/blendmodes.htm

http://northlite.50megs.com/ps/blend.htm

http://teamphotoshop.com/articles-The-Techniques-Fun-with-blend-modes-5,8,62a.html

http://www.romeo-help4u.com/MG/tutorials/PS/site/basics/?page=blending-mode

http://www.nebulus.org/tutorials/2d/photoshop/ps3/

http://www.debdsweb.com/tutorials/blends.htm

http://www.gatheringofartists.com/epitome/content/index.php?option=com_content&task=view&id=89&Itemid=52

http://www.gatheringofartists.com/epitome/content/index.php?option=com_content&task=view&id=77&Itemid=61

More Advanced

http://www.worth1000.com/tutorial.asp?sid=161017&page=1