If the Moon Were Only 1 Pixel is a tediously accurate model of the Solar System that Josh Worth made to explain to his daughter just how difficult it is to go on holiday to Mars.
Tekhnika Molodezhi was the Popular Mechanics of the Soviet Union. The magazine, whose name means Technology for the Youth, had illustrations of everything from space stations, computerized farming, transport of the future, friendly robots, to more abstract images. If you don't want to hunt through the archive, Mythbuster's Tested website has a gallery of 201 great images from the magazine.
Auroras Underfoot is a short documentary about auroras by NASA, which uses high-definition images taken by International Space Station science officer Don Pettit of aurora from orbit. Pettit writes about the difficulties of taking photographs from orbit and other subjects on his blog.
The Habitable Exoplanets Catalog is a database of the planets outside our solar system which are considered the most suitable for life according to certain steps and metrics. So far 16 have been identified as possible candidates. This Guardian article is a good introduction. You can also just dive into the catalogue, which ranks planets on two main scales, similarity to Earth and surface habitability (note that all images are computer renderings). The catalog is a project of the Planetary Habitability Laboratory at University of Puerto Rico in Arecibo (home to the world's largest radiotelescope).
Cosmic Journeys is a documentary series on various astronomical and space-related subjects, e.g. supermassive black holes, Apollo 12, whether the universe is infinite and many more. The creators, SpaceRip have a lot of other, shorter videos online as well. They are indexed here. Most, if not all, of the videos are available in HD.
"I can sense stars, and their whispers amid the roaring of our own Sun." So goes one poetic status of the Voyager 2 twitterfeed, which appeals to my sense of wonder like nothing else on the internet. Interstellar space probes and microblogging go hand in hand in the 21st Century.