Wow, Buzz Aldrin is on Twitter twitter.com/TheRealBuzz
A few NASA (and non-NASA) astronauts are also on Twitter and have been tweeting from the International Space Station (ISS). According to the website, currently at ISS are astronauts
Jeff Williams (Twitter - Astro_Jeff)
T.J. Creamer (Astro_TJ)
Soichi Noguchi (Astro_Soichi)
It seems that Jose Hernandez (Astro_Jose) has also been tweeting from space.
I've been following most of them for the past few weeks and Soichi's twitpics (photos) from space over the past two weeks have been amazing.
Sydney, Australia (two hours ago)
Thanks to Claire O'Neill at NPR for the prompt.