The Washington Post is out with a list of the best architecture of the decade here: http://www.washingtonpost.com/wp-dyn/conte...9122400116.html
The Tate Modern in London
National Stadium in Beijing
The Walt Disney Concert Hall in Los Angeles
The Seattle Public Library
Alice Tully Hall in New York
I saw the Seattle Public Library a couple of months ago, and it is a great structure. Very modern, but very welcoming and heavily used by the public.
And unlike my local library which won't even permit bottled water inside, the Seattle library has a cafe and a gift shop. Finally, a public library that realizes it has to compete with Borders and Barnes and Noble and that there's no shame in giving people what they want.
I saw the The Walt Disney Concert Hall earlier this year, too. It's a great space, but not so welcoming. It invites you to get close, but not too close. Still, there are great places inside and a nice little cafe.
I don't necessarily agree that the Tate modern should be on the list, mostly because it's the reuse of an existing space.