In Photoshop CS3.
Involves Selective Coloring.
01. Resize first (of course). Go to Filter>Sharpen, and then to Edit>Fade Sharpen>50%. But make sure your image doesnt get too sharp, if it does, you can fade it to less (or more if you image is blury), for example 25%, or you can just not sharpen at all.
02. Dublicate your image (by right clicking on the layer in the layer panel), and set it to Soft Light 100%. NOTE: If your image is too dark, you can dublicate your base and put it on Screen 100%, if its still too dark, you can dublicate the Screen layer as many times as nessecery.
03. Make a new Selective Color (this makes the main diffrence in this tutorial) layer, with something along these settings:
REDS: -100, 0, +100, 0
YELLOWS: +100, 0, -100, 0
NEUTRALS: +21, 0, -1, 0
I think many tutorials starts of with these settings, if you'd like the coloring to be more neutral you could lower the opacity on this layer, or for example make the -100 to -50, ect.
I dublicated this layer once.
04. To make it a little darker, I made a new fill layer with the gray color #dddddd, And put it on Multiply 100%,if you don't want the coloring to be darker, you can just skip this step.
05. Now, to do something about the contrast, make a new Levels layer. This time I only used the RGB channel, but if you'd like to make other colors pop out more, you can try the other channels aswell.
I used these settings:
Input Levels: 7 - 1,19 - 255
Output Levels: 10 - 232
06. Now, to make it more colorfull, make a new Hue/Saturation layer. Boost up the master Saturation, I put it on +15.
NOTE: Hue/Saturation can make the coloring too red, if so, lower the opacity on the hole layer, or make the saturation lower, by using a lower number, for example 5 or 10. Or, you could of course just skip this step.
And now you're done!
Here's some other examples of this coloring: