VideoForEverybody
In theory, nothing could be easier than sticking a video tag into your HTML. In practice, the behavior of so many supposedly standard-compliant browsers is different enough that you'll be pulling out your hair if you try to support all of them. A number of good HTML5 libraries let you write standard HTML5 video tags that will be replaced with Flash or QuickTime if the browser isn't ready to handle your video. The Video for Everybody project offers one of the better libraries, filled with features that operate in the background to smooth delivery on older browsers like IE8.
