To accompany his latest book on Flash Video, Robert Reinhardt has developed a awesome bitrate calcuator you can use to figure out target bitrates for your web video.
Also, if you haven’t read his latest book, be sure to check it out. 5 Stars at Amazon! Here is a brief description:
From pre-production to post, author Rob Reinhardt shares the techniques that make Adobe Flash a powerful tool for sharing video over the Web. With sections on capturing and encoding video, creating and using cue points, working with transparency, and deploying and delivering optimal quality, he covers the information that users need to get started, and then goes in-depth to bring his readers to expert status quickly.