I really like this project. One of the few things that the government seems to be getting right at the moment.
If you've not already seen them, the BBC's design guidelines are also very good (though obviously somewhat different in scope): http://www.bbc.co.uk/gel
If you've not already seen them, the BBC's design guidelines are also very good (though obviously somewhat different in scope): http://www.bbc.co.uk/gel