This is just unbelievably cool.
What to follow
You can follow NASA here for general NASA tweets, but more importantly, they have a list of astronauts currently in space. Follow that list for lost of fantastic pictures and videoes live from the ISS.
You'll see a lot of tweets by Japanese astronaut Soichi Noguchi (I highly recommend you at least follow him), containing amazing images from space.
To give you a few examples of the coolness that is live images from space, here's a few pictures from Astro_Soichi (his original tweet text is in italic).
(The pictures are all from February/March 2010, but his tweets go back further)
Pictures of our Earth
I'll start with some pictures taken down from space of places on Earth you may or may not recognise.
YES, you can see pyramid from space :-) Late afternoon in Egypt.
Uluru, Australia. In the morning light. Big rock. I mean, a huge rock.World heritage. Sacred place.
Big water falls in Zimbabwe
Sorry folks, you may be tired of seeing this, but I cannot stop shooting Patagonia Glacier.This is not a scene from Avatar - this is the real world!
What is this? Gold mine? South-west Australia.
Easter Island. World heritage. Isolated island in south Pacific. Famous for Moai!
Pictures of space
But you can also take cool pictures of space when you are aboard the ISS.
Full Moon high up in the sky.
Moonrise right over horizon.
Or you can shoot a video of the Moon setting in the horizon. It's an amazing sight and it happens really quickly when you travel at 27000 km/h.
I uploaded a YouTube video -- moon20100301_0001.wmv
How to see more
If you aren't using Twitter, here's a reason to do so.
Or if you are using Twitter but aren't following NASA and the astronauts you now know why you should :)
If you don't want to use Twitter, you can check out Astro_Soichi's pictures here at Twitpic and his videos here on Youtube.