There are actually several brands of pressure-sensitive styli available for the iPad, including Adonit Jot Touch, Hex3 JaJa, and Wacom's own Intuos Creative Sty

There are actually several brands of pressure-sensitive styli available for the iPad, including Adonit Jot Touch, Hex3 JaJa, and Wacom's own Intuos Creative Stylus, and even more on the way such as the Hex3 YuFu and Adobe/Adonit's Project Mighty, though it does appear that none these offers come close to devices with actual Wacom active layers built-in, as most of these pens are bluetooth hacks that attempt to make up for iPad's shortcomings. It's really a shame, though, since I find iPad's library of note-taking and drawing apps to be significant better in terms of quality and quantity than those found in Android's Play Store and Microsoft's Windows 8 Store.