I felt like promoting this one because..well it's free.

http://firealpaca.com/

I love the smooth lines I'm getting from it, and while limited I do like how you can move the palettes around or take them off if you don't want them anchored to the dock.

Now there isn't fancy brushes and they're very simple, but I think this can be a good recommendation to get beginners to stick with basic digital tools, and this is user friendly enough.