If you haven't checked it out yet, you need to take a look at Seadragon.  I know its from Microsoft, but I like it anyway!  Seadragon is a software project to allow users to browse and zoom into high-resolution images.  I'm especially attached to the iPhone version of 

Seadragon Mobile (link opens iTunes) available for free from iTunes!

One of the best things about the iPhone version is that it includes some example images, and includes some of the work from Chris Jordan.  Longtime readers of the blog know I really like Chris Jordan's series "Running the Numbers" which uses high-resolution images to visually show the viewer statistical information about how we live.