Paper by Fifty Three
Sketch on virtual paper

Painting app

ArtStudio (£2.99)
Sketching, painting and photo editing tool

Drawing app

Sketchbook Pro (£2.99)
Full featured drawing app

Musee du Louvre
Louvre works of art

How to draw Manga
Manga tutorials

Doodle Buddy
Finger painting

Starry Night Interactive App
Van Gogh's Starry Night with interactivity