The subtle art of image manipulation...

I came across some well done Photoshop tips, tricks, and tutorials in a series of posts over at LifeHacker.

The first link covers popping pimples, whitening teeth, and changing a person expression, essentially "altering reality as we know it".

You can also find two posts on "learning the basics" a quick down and dirty 25 minute version and a longer, more complete guide. There is also a downloadable .pdf file that is a combination of the two.

And lastly (there are more but the last one for this post) this post covers color corrections, touch-ups, and enhancements.

Go check out LifeHacker for anything and everything related to technology.