Image content-aware resizing
I just came across this video demonstration of some clever image manipulation research presented at SIGGRAPH 2007 by Shai Avidan and Ariel Shamir of Mitsubishi Electric Research Laboratories (MERL).
The video shows off a method they call "Seam carving", enabling content-aware resizing that changes the size of an image according to its content. You've got to see it to believe it.
(Their original paper (PDF) provides loads more detail on the research)