Well, after several postponements, Endeavour may be launching tonight at around 11.03pm. Or it might not, cos the weather's been a bit iffy.
Anyway the countdown is shown here:
Space Shuttle Countdown Portal - Welcome
but the best bit is if you pull down the "Launch Streaming Video Feed" menu on the upper right. This gives you NASA TV, which I have found absolutely fascinating. It gives all the up to date info, and with cameras on the Shuttle and the gantry, shows the crew being suited and booted and explains the process, as well as giving info about the payloads, mission etc.
It will run in the background so you can go off and do other things, and your computer speakers will suddenly burst into life if anything is happening.
Lets hope she gets of safely tonight.
ps. A friend of mine saw a Shuttle Launch in Florida a few years ago, and said there is no way you can imagine what witnessing a launch is like. The noise (and the spectacle itself) is just mind blowing. I doubt my computer will do it justice!