Inkling can store thousands of sketches and export layered files directly to Adobe Photoshop and Illustrator (CS3 or newer), as well as Autodesk Sketchbook Pro (2011).

ENGADGET: Wacom Inkling smart pen does drawing the old-fashioned way -- sort of (video)

Apps include: Brushes, Zen Brush, PDFpen for iPad, Procreate, FlipBook HD, Sketch Club, SketchBook Pro, Art Studio, Good Notes, Colors, Paper by FiftyThree, Noteshelf, NotePad Pro, NoteBinder, IbisPaint and ArtRage.

ENGADGET: Ten One ships $80 Pogo Connect, a pressure-sensitive Bluetooth 4.0 stylus for iPad