Apple has posted more than 100 session videos for WWDC 2012. They are available on their website for free, but you must be a registered Apple developer. The good news is that the registration itself is free. However, the license will run you $100 (but that’s only useful if you plan to release an app or want to download beta version of iOS)
Otherwise, you can check out the session videos by signing up and logging in. If you are already a developer, then just head on over and login to watch.