Velvia

Just a try to get vivid colors something like Fujifilm's Velvia film using free software GIMP. Although you can use Hue-Saturation tool to increase color saturation, the following method is closer to Velvia. Another reason is that Saturation can sometimes posterize color. Open the picture you want to edit. Open Colors menu -> Compoments -> Channel mixer....

Choose Red in Output Channel and increase Red slider to 150. Reduce Green and Blue sliders to -25 to balance it. Repeat the similar steps for Green and Blue channels.

Output Channel: Red
Red: +150
Green: -25
Blue: -25

Output Channel: Green
Red: -25
Green: +150
Blue: -25

Output Channel: Blue
Red: -25
Green: -25
Blue: +150

Click OK. Then choose Colors menu->Levels and increase the slider below input levels until you get a desire contrast.
After that, you will get a Velvia style photo. See the following pictures as a comparison between original and Velvia style.

Before
After

Reference:
http://photoshoptutorials.ws/photoshop-tutorials/photo-effects/velvia.html