I received the "Pogo connect" (from TenOne) yesterday, which really is above my expectation. Basically it is one of the few pen that actually can manage pressure and anyone who ever used a tablet before for drawing and painting knows that this is the really important thing you need for a good drawing experience. So basically it connect through bluetooth 4.0 (so iPad 3 and 4 only) and send the pressure information to the iPad and the app. I had a wacom tablet for a while now, since i am an amateur "photoshop painting artist" and I must say so far that I am really impressed by how well the Pogo Connect work on the iPad compared to my wacom tablet. In a way I feel like this combo is kind of a more affordable portable high res Cintiq. The cheapest Cintiq display start at 999$, and the screen is nowhere near the quality of the one of the iPad. Anyway its a good thing that Wacom finally is challenged by serious competition. Especially since the iPad is also a way more versatile device in general.
About Apps, i tried Sketchbook Pro and Procreate, and i must say that by far Procreate is the best one of the two, and from the reviews, clearly one of the top painting app for iPad. It's a very well designed app, the interface is really well done, easy to use, easy access to the tools and brush you need, has everything a good image app need, like layers, lots of "undo", lots of customizing options for brushes, very useful gestures, and on top of it, it is really really fast. I see almost no delay at all even when using complex brushes and pressure dynamics with the Pogo Connect. Good export and importing option including very good Dropbox integration. And to top it all, it is only 4,99$
It can work with 4096x4096 images (although the image resolution limit the number of layers you can have. The minimum being 4 for a 4096x4096 image and it can go up to 28 for smaller images.)
It is a very well crafted app for a very affordable price. For me this app is a no-brainer for anyone who wants to sketch and/or paint on the iPad.