one more trick, create a line (as thick as you want the ripple/crease), preferably straight but it still does work if it spawns off into other directions, and put it in a new layer. bevel it with the layer effects of photoshop, mess around with contour and other settings within bevel (texture usually isn't necessary but if you make a good one it'd be really purty

) until you get something you like.
example: (btw...this is a 3d model i made, clothing was touched up a bit in PS6, and the eyes are textures made by me in photoshop as well)
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