This thread has an excellent discussion of video format conversion and formats for the web....
What are my Options to Convert .wmv? I need cross platform compatibility. [webmasterworld.com...]
As you may already know, Flash has become the de facto cross-platform web standard, largely because of YouTube. It's very expensive to host Flash video yourself, though, so most small sites use YouTube for hosting and embed a player in their own pages.
When hosting on YouTube, it's wise to add your own site's titles and identifiers to the video. This may create some issues with the manufacturers who produced the videos.