There are a lot of iPod Touch and iPhone apps now. And, of course, there are inevitably a good number of drawing apps. My favorite so far is NetSketch, not necessarily for its ability to share the sketches you make with others, but for its color and brush choice (though I honestly wish I had a lot more brush choices), and for its zoomability, and because it saves everything not as raster images, but as curves. And you can convert your finished drawings to eps files for messing with in Illustrator (or some other eps-able software).

Neato. Though I'm still holding my breath for something just a tad more painterly, this one is doing right by me for the time being.