SkyCat (http://archive.eso.org/skycat)
accesses the HST, ESO NTT and CFHT archives to retrieve images and displays
them with a variety of options to identify objects on them
Astronomical Digital Image Library
(http://imagelib.ncsa.uiuc.edu/imagelib.html
contains "books" with FITS images taken at different wavelengths. It
provides a convenient way to archive and distribute the data.