Unsharp mask unveiled
http://www.naturescapes.net/docs/index.php/category-image-editing/37-image-editing/350-unsharp-mask-unveiled
High pass sharpening
http://www.youtube.com/watch?v=K9VXeOKLvgs
The power of curves
http://www.youtube.com/watch?v=ORM6AZY19pw
Using curves adjustment in photoshop
http://www.geofflawrence.com/photoshop_curves.html
Using levels adjustment in photoshop
http://www.geofflawrence.com/photoshop_levels.html
Full control in Photoshop: layers and layer masks
http://www.naturescapes.net/Joomla1.5/index.php/category-image-editing/37-image-editing/66-full-control-in-photoshop-layers-a-masks-
Awesome eyes in Photoshop
http://www.youtube.com/watch?v=-kIkarvhoa8
Adding dramatic colour to photographs
http://www.youtube.com/watch?v=eneyl4KS99A
How to resize an image
http://www.youtube.com/watch?v=qu5adJfxuhw
How to photoshop a person into a picture
http://www.youtube.com/watch?v=TbDL6b97kY0
How to use Photoshop to refine an edge
http://www.youtube.com/watch?v=TcZkvF9pLrE&feature=related