Yesterday I found ArtRage, a digital painting program and used it to colour this robot drawing.
(I've been trying to find replacements for Photoshop, which is very expensive to buy new.)
I was looking at GIMP, which is a free open source program. I really didn't like GIMP very much and found it really frustrating to work with. It has a lot of the features of Photoshop, but I got too frustrated trying to figure out how to use it.
Then I found ArtRage, and the demo worked well enough that I bought it. ($59 compared to PS's $799)
The ArtRage app and UI is designed well and if you're used to colouring in Photoshop, then it all translates really well. You can paint in layers, and as you can see, you get a really nice effect with the oil brushes. Next I'll have to try out the inking and the watercolours.
It does have some drawbacks and isn't really a Photoshop replacement. It can't open more than one painting at a time, it's doesn't have Photoshop's gradient tool, and it can't record actions and apply them to a folder full of images ( very handy for resizing your digital photos for web uploading ), and importantly for my photo documentation of my paintings, it can't correct lens distortion. However, what it does do, it does well, and it's well worth the purchase price.
Now I just have to find something that can open the NEF files from the Nikon and do batch resizing on them and also allow me to correct lens distortion, and stitch together composite shots of paintings, then I'll be all good. Yikes, I might just have to buy Photoshop anyway...