Videos from the vault of the National Archives -- the public domain US government videos that public.resource.org have been scanning. Check out China's Great Leap Forward (the Beijing landscape has changed!), John James Audubon's Birds of America, and Nature's Half-Acre.
Browser Market Share -- fantastic circular visualisation of browser share over time. (via Mike Loukides)
NYT Year in Ideas -- some fantastic stuff, but I think my favourite is Zombie Attack Science.
dygraphs -- Javascript library that creates gorgeous zoomable graphs of timeseries data.