The commit feeds provided by github only list the files that changed, and do not include the diffs; github-rss fixes that. It is a simple web service that acts as a proxy and uses the github API to fill in the diff for each commit in the feed.
To use, simply give the app your feed url:
http://github-rss.example.com/?feed=https://github.com/username/project/commits/master.atom
You can also use it with private repos, but you'll need to provide your login and token, and you'll need to escape the '?' and '&' in the feed url with '%3f' and '%26' respectively, like so:
http://github-rss.example.com/?feed=https://github.com/username/project/commits/master.atom%3flogin=my_login%26token=1adefed234
Issues and pull requests welcome!