Lots of generic hosting providers can be used for it too, if you have a hosting account somewhere. As long as the server has git and you have SSH access, you can do this on the server side:

$ mkdir project_name.git; cd project_name.git; git init --bare

Then locally, from the repo directory:

$ git remote add origin username@server.com:~/path/to/project_name.git

That's what I do (on Webfaction). Of course, then you don't get all the fancy issue tracking and all that from github, but it works if all you need is a few kb of storage for a remote. That also makes it easy to deploy PHP projects with a single post-receive hook, since it's all in the same box.