@kinggp It depends. If you want to watch specific races on demand, I suggest you check out YouTube and Youku. YouTube is the site we all know and love, but is usually only good for races from the 50s to the 90s. Youku is China’s answer to YouTube and has some of the more modern races that are usually blocked or taken off YouTube altogether.
Personally, I prefer watching races at random (i.e. I’ll watch whatever you’re broadcasting). For that, there is a channel on Justin.tv that does just that. But I don’t want to paste the link here as that usually leads to a takedown later. I suggest you search “F1 Legends” on Facebook instead. Once you find the page, you should be able to find instructions to access the channel (as well as the password to the channel).