I love Poly. This iPad app allows you to draw points on any photograph, turning it into a colourful mosaic of polygons. The effect is really pretty. Sadly, it's optimised for iPad 2 and runs slow on the first iPad.
According to the author, it's "inspired by the Triangulation invented by the mathematician Boris Delaunay in 1934. Well, thanks Boris, because this is a lot of fun. [iTunes via mocoloco]