Art Project, powered by Google is an online resource that allows you to "explore museums from around the world and discover and view hundreds of artworks at incredible zoom levels." This powerful resource lets you explore the museum floors (similar to the way you navigate on Google Earth) or just view the artwork. New users should click here for an overview about the site and how to get started.
Check out some of the museums on the list, which are some of the best in the world!
Google will continue to add locations so check back often.