A fantastic visual representation of the scales of the universe, from galactic clusters to atomic nuclei and beyond. (Requires Flash.)
The Last Mechanical Monster is an Eisner Award-nominated comic following the story of a mad scientist in his twilight years, reflecting on the nature of mortality and the legacy we leave behind.
Duolingo is a great website for learning a new language. Learning objectives target your speaking, writing, and reading skills. I'm using it to improve my German.
A Soft Murmur is an excellent source for soft background noise--rain, a campfire, singing bowls, etc.--perfect for working at the computer. Noisli is another good one, with interesting options like blowing leaves.