PocketSketch, a graphics/drawing application from GonnaSoftware, looks like it's got pretty much the standard functionality you'd expect for this type of software, like an easy-to-use interface and a broad palette of colors.
However, it also has a couple of features that I've not seen in this kind of software before. First, it includes dozens of "stamp" images and icons that you can easily insert anywhere into a graphic. Second, it integrates with Inbox so you can easily send graphics via e-mail. PocketSketch only supports BMP and JPG formats, but the stamping feature might make this fun to have on hand for doing some light-hearted doodling.
Reminds me a lot of the telecard features in Magic Cap from the mid-nineties. I always loved that; it was so much fun to send handwritten sketches with stamps by email or fax to friends.