What do you do if you are storing projects on a Github Repo that contain a private API key?

I think I speak for most web and mobile developers when I say we've all needed to work with API's at some point. The thing is, if we are doing small scale projects that are kept on public repositories, what should we do to protect our API keys?

We dont want people having access to our personal keys, especially if there is a daily or monthly limit imposed, or the API's are used to access important sensitive data such as financial or customer information.

It seems pointless to go through the project and remove the key from the code all together everytime you commit, especially when you have multiple API keys being used in the same project. So I want to know what you guys do in this situation.

Thanks