Here’s a great Photoshop action that reproduces the look of “Amelie” (one of my all-time favourite movies, and I say that as a dyed-in-the-wool, lifelong, lifesucks cynic) on your images. Regardless of whether one judges it to be an effective reproduction (you probably have to pick the right chocolate-box kind of images), it also helps to brighten up dull colours. Even better, Dawn gives you the manual formula so you can use it in other applications (like the GIMP).
Unfortunately, due to bandwidth constraints, she took her site temporarily offline at the end of last month, just when I wanted a reminder of this technique. And I couldn’t find a mirror anywhere, only links (even Google didn’t cache it, due to the headers). So here’s another copy of the recipe: 1. Duplicate the layer with your image on it. 2. Set that layer’s Fill to 50% and the Layer Mode to Pin Light or Overlay. 3. Open Color Balance. 4. In Color Balance, select Hightlights under the Tone Balance section, then change the Color Balance to 5, -20, -100.