Covers curves, levels, and contrast; the basic adjustments all photographers need to do. Also see here on YouTube. For a screenshot of the detail being discussed, click to view here.

Uses some very basic adjustments most photogrpahers use for minor adjustments, but never for the extreme examples used here (these won't look natural). Uses Levels, and Highlights

Effectively isolating the subject from the background using Colour Range, and Expand Selection.

Using levels, layers, and quick mask

Using layers, quick mask, and replace colour

Using selection, layer masks, artistic plastic wrap filter, blending modes

An essential tutorial (highly recommended). Using layers, cutting out with polygon lasso, layer effects

Using curves (with colour channels), layer mask. This is recommended as his use of curves is a great example. Also see this one that uses quick mask.