I have recently found codecov; they offer free services for public GitHub projects. As I have recently started writing tests for my SWE-GLib project, I decided to give it a go. Things are not this easy if you use GNU Autotools and libtool, though…
The problem here is that these tools generate output under src/.libs/ (given that your sources are under src/) and gcov has hard times finding the coverage data files. Well, at least in the codecov environment, it works fine on my machine.