To help demonstrate "the importance of image file formats for digital art", Kim Asendorf has created a handful of esoteric formats (4bc, bascii, blinx, cci, mcf, uspec, xff) and an application to convert between them and their more common bretheren (jpg, tiff, etc).
I had the honor of being part of a team of beta-testers / format hackers, and can attest that the new formats are a lot of fun to explore. By expanding the number of available image formats, they inject new life into the field of text / hex image hacking. The ExtraFile application is also a handy tool for general databending experiments, as it automatically refreshes the displayed image each time a change is made to the image's source code.
The project has now been made available for the public at extrafile.org, so download it and start experimenting! Descriptions of the new formats are available on the project site.