Last year I developed a web app called "Whatsdeployed" . It's one of those rare one-afternoon-hacks that turns out to be really really useful. I use it every [work]day. And I've heard many people say they use it too.
At the time I built it, it only supported comparing multiple instance. E.g. a production and a dev site. Or a test, stage and production. But oftentimes, especially for smaller projects, you might only just have your one deployed site.
So I've now made it possible so you can compare just 1 site against your github.com master branch.
For example: whatsdeployed.io/s-Sir
What these do, is simply comparing what git sha revision is deployed on those side-projects, compared to the latest git sha on the master branch on github.com.