Lunar eclipses are common, happening twice every year but, tonight's one is supposed to be the best one ever. We should see the moon turning a red colour like Mars according to the BBC website. Quoting:

"The eclipse begins at 2018 GMT, with the Moon totally immersed in the shadow of the Earth between 2244 and 2358 GMT."

This should be fun to see. The next lunar eclipse should be February 2008 if you miss this although it might not be so spectacular.

Update:
Bah, I couldn't see a thing because of all the clouds! I did see the moon going a mouldy yellow colour when it was half gone, though...

Source:
• BBC News