PBS
Pbs Learning Media: Sagan on Time Travel
Astronomer Carl Sagan discusses the possibility of time travel in this audio-enhanced interview from the NOVAWeb site.
NASA
Nasa: Fall Into a Black Hole!
This site from the National Aeronautics and Space Administration allows one to play "Falling into a Black Hole," and take an imaginary trip to a black hole right now!
NASA
Nasa: Imagine the Universe: Black Holes
Resource introduces black holes at two different levels. Take a journey through a black hole, discover what a wormhole is, and discover how we know black holes are there. Includes a quiz on the information presented.