These days we have embeddable share and follower buttons for almost every aspect of the web, except of course for GitHub. I wanted to help remedy that, so over the weekend I created a customizable JavaScript button (that uses the GitHub API) for pulling in the watcher counts for links to any repositories you may have in a page. It gracefully degrades, comes in a few different flavours and is available to get now.
All that's needed to use the button is an a link to a specific repository (such as http://github.com/h5bp/html5-boilerplate). It doesn't need to be on your account, it can belong to anyone (which is particularly useful for groups and organizations that share repositories) and it's flexible, so it should work regardless of whether you have 8 watchers or 8,000.