Gimp

Layers->Colours->Curves is another handy thing for tweaking images. It can be used to improve the contrast of the things that matter in the photo slightly, at the expense of the things that don't.

Straightening, cropping, curves and unsharp mask are the things I use most often. It's easy to overdo unsharp mask though, so I usually turn the controls down until it isn't really making much of a difference in the preview, then turn them back up a little bit.

Oh, and the cloning brush too, that can be very handy.

Robert.

It is daunting to start with, but then so is photoshop. With a few tutorials or a good book it is not so bad and certainly a great package for free.

High pass filter, good for non-destructive sharpening, needs adding to the program. (it did in 2.6) http://registry.gimp.org/node/103

Create a duplicate layer.
Desaturate
Perform high pass filter.
Change to overlay