[Update: The Shuttle launched right on time in a picture-perfect lift-off. It's on its way to the space station, and is scheduled to dock on Tuesday.]
The Space Shuttle Discovery is scheduled to launch at 19:43 tonight Eastern time (23:43 UT). It will go to the space station and, among other things, install solar panels which are expected to make the ISS the third brightest object in the sky, after the Sun and Moon, brighter even than Venus.
I'll be covering the launch on Twitter as usual, except that I'm trying something new: I've created a new account called BANews that is just for breaking astronomy and space news. It's just an experiment to see how people like it; this way people who follow my regular feed don't have to see 40 updates in an hour from me. I'll post a handful of times from my regular feed so people know to sign on to the other one. You can also follow NASA and Miles O'Brien for more Shuttle info. You can also watch online at NASA TV.
Anyway, as I write this, the external tank has been filled and there's no sign of any dangerous leaks. The crew is filing on board, and they're prepping for tonight's launch of STS-119.