The other day I tried out the free demo of "ArtRage 2" (link) and within the first ten minutes of playing around with it I decided to buy it. Not a huge investment – only $19.95 compared to $199 for "Autodesk (formerly Alias) Sketchbook Pro" – but one that I think will be well worth it. The interface is fantastic and easy to use and while it might not be as configurable as "Sketchbook", there's still a LOT you can do with it. And, while it's nice to have a tablet to use with it, it isn't necessary. It's not going to replace Photoshop for me, but it'll make a very nice addition for when I'm in a "natural" media mood.
Comments, as always, are welcome.