Apple has now posted the video of its keynote held earlier today in Cupertino. The video can be streamed here, and a higher quality version should be made available in a few hours through iTunes (on the Apple Keynotes podcast). To avoid streaming errors, Safari is recommended for the best viewing experience.
Update 10:50 PM EDT: Today's keynote video can now be downloaded in standard definition through the Apple Keynotes podcast on iTunes. 720p and 1080p versions will likely be released tomorrow.