How do I get notifications for commits to a repository?

Subscribe to Github's RSS feed!
Choose your news feed (all watched repos), or only Lithium's commit history.

RSS are made for that ;-)

PS: I don't see how can you find that useful since there is a couple of commits made each day on various branches, some small typo fixes, others fix bugs, and others introduce new things...

I just found out by accident that you can easily manage to achieve this:

• fork the project (if you haven't done it yet)
• create a pull request for yourself from the selected branch, e.g. from master of head project to master of your fork:
  • base repository: your/project ; base: master <-- head repository: original/project ; compare: master
• do NOT merge this pull request
• under the Email section of your Notifications settings enable:
  • Comments on Issues and Pull Requests
  • Pull Request reviews
  • Pull Request pushes

That's it. You will receive email notifications about every commit on master branch.

In addition to the other suggestions, you might try HubNotify for e-mail notifications.