Google does it again (Google Art Project). A fantastic application of their existing street view technology applied to some of the world's most amazing art collections and museums. I know, it still isn't the same as being in the same room as these works, smelling the sterilized air, pushing past crowds and searching for the restroom, but it comes close.
Sign in and you can create your own art collections from their works and share your collections with your students.
Now I am thinking Google should apply their street view to the skies (astronomy) and the microscopic - DNA, molecules, the dust mites under my couch.