Guile-Cairo is complete, wrapping almost all of the Cairo API. It is API stable, providing a firm base on which to do graphics work. Finally, and importantly, it is pleasant to use. You get a powerful and well-maintained graphics library with all of the benefits of Scheme: memory management, exceptions, macros, and a dynamic programming environment.
Guile-Cairo has changed hosting providers, moving to savannah, where you are probably reading this message. A new release has been made, in order to link to the new location of the git repository, and other such things. Version 1.9.91 is still a prerelease. Give it a try!