Are there any examples of a government department successfully using social media?

By social media, I mean things like Twitter, Facebook, MySpace, Youtube, blogs, and Wikipedia.
Any country or level of government is okay.
I’m doing a presentation and need some examples. Thanks.
Obama is an interesting example, but I’m thinking more along the lines of a department, rather than a specific individual or politician.

The president of the United States. He has used youtube lots of times, posting his daily speeches on there sometimes.

That’s my answer, Barack Obama.