(Yikes! So sorry about being late with this; with the fall term beginning I got overwhelmed with getting all my syllabi and such prepared.)
This effect is quick and easy, yet can add real punch and drama to even a mundane image. This is the effect I used in the image Gettin' High in Low Places I'm looking forward to seeing the creations you come up!
You will create three adjustment layers; the easiest way is to use the Layers panel, but you can also use the Layer drop-down in the main menu.
Duplicate your image (Ctrl-J), making Layer 1 (not necessary but I like to preserve the original).
Create a Hue/Saturation Adjustment Layer and bump the Saturation up to 30 or so.
Click Layer 1 and create a Brightness/Contrast Adjustment Layer; increase the Contrast to 30 or more.
Click Layer 1 again and create a Levels Adjustment Layer. In the Channel drop-down select the Red channel and drag the middle gray slider to the right until there is a noticeable green cast. Now select the Green channel and drag the black slider to the right and/or the white slider to the left to increase the contrast a bit more.
You can flatten the image at this point, but I prefer to select the top layer and create a stamp layer (Ctrl-Shift-Alt-E).
Add a vignette to finish: Select Filter | Correct Camera Distortion. Under Vignette, set the Amount to about -60 and the Midpoint to around 30 and click OK.