picnik

I tested a little bit with this image:

dscf4245

I played a little around, and what came out was this:

great sky

After that I fired up GIMP and fiddled a little with it:

dscf4245 gimp

I only adjusted contrast, thats all .. (I did a little to much here, I know).

So if you are new in photo editing or you have not the possibility to install your favourite photo editor, picnik is an option. If you really want to get behind the things, learn to work with a real image editor.