forget all the answers, this line of CSS worked for me in 2 seconds :
1vh = 1% of browser screen height
For responsive layout scaling, you might want to use :
[update november 2018]
As mentionned in the comments, using the min-height might avoid having issues on reponsive designs
[update april 2018] As mentioned in the comments, back in 2011 when the question was asked, not all browsers supported the viewport units.
The other answers were the solutions back then —
vmax is still not supported in IE, so this might not be the best solution for all yet.