The ArtRage app from Ambient Design is $4.99 for the iPad and $1.99 for the iPhone, with Studio versions for more serious artists available for Macs and PCs ranging from $19.90 to $49.90. Find out more about them at artrage.com.
The GoSmart Freedom Stylus is $23.95 and available at http://justgosmart.com. If you use your device to write notes, this one comes closer to a true pen-to-paper feel, once you get used to the metal tip. The squishy tipped-styluses, including the HAND stylus I have written about, work, too, but I like them for navigating touch screens and typing on keyboards.