Check out this fantastic collaboration (from LifeHacker) of learning opportunities from .edu websites; they are categorized in Art, Science, Space, Humanities, Photography, History, & Misc.Here is a sample of the entry for .edu opportunities in Science:
Explore gross anatomy at the University of Michigan Medical School. Download a virtual microscope at the University of Illinois at Urbana-Champaign (you can look at 90 different samples; anything from algae to aorta). There’s also the University of Connecticut School of Medicine’s Pathweb, a virtual pathology museum. Go Ask Alice from Columbia University is a health Q and A site. Identify flora and fauna with the help of Louisiana State University’s Herbarium. Find folk medicine remedies from nature at the UCLA Folkmed Database.
Of course, check out the comments section at the bottom to see what their readers also feel worthy to add to the list.