Grunge Effect, etc.

How do you get the coloring effect on the following icon made by _velvetdivorce?


And I know this may be a very broad question, but I hope the examples somewhat help you understand my question.
How do you make icons with a grungy effect (cropping, coloring, etc.), like the few following (the ones below are all examples. if this question has already been ask, is it possible for you to direct me to a tutorial of this sort? i have already searched the memories and found no luck)?


 by iqons
 
 by unstamped
 by autofade

Thanks in advanced =D