This is a great tip for weak color channels. For example, if you shoot something red (flowers for example) you will notice that you dont see any detail in the reds. Heres how to fix that.
Step 1: go to your channels window and click on the red, green, and blue channel seperately (or use ctrl 1,2,3 and the tilde key to get back to rgb).
If a channel is weak you will see alot of white and no detail.
Step 2: choose the channel that the detail looks best in. For weak reds the green channel is usually the best.
Step 3: go to window - layers and duplicate the background layer.
Step 4: highlight the background copy layer and click on the weak channel in the channels palette. You should now be viewing the background copys red channel for example.
Step 5: go to image - apply image.
Step 6: here is what you want the settings to be in the apply image box.
layer - background
channel - green (or whatever channel had the best detail in it)
blending - normal
opacity - 100%
Step 7: hit ok.
Step 8: go to your layers palette and change the blending mode of your background copy layer from normal to luminosity.
Step 9: make sure in the channels palette you are on rgb (you want to be viewing all the colors)
Step 10: lower opacity of the background copys layer till it looks good.
note: you could always make an action of this to use in your workflow.