The one on the Fairey poster. That's what I used for the one I posted.
Aha! Now I can put my internet-addiction to good use!
The typeface Fairey used is actually one called
Gotham - it's the typeface that Zero used for most of his lying (I mean campaigning) in 2008.
Arial bold is a pretty decent work-around for Gotham (which does not come cheap - unless one knows where to look
); another free typeface that does a reasonable job of approximating Gotham is
Nevis. I was lucky enough to get access to Gotham, so I've used it.