GNOME-specific tools for the C language
Related Tools section in the GObject API reference
Builder: an IDE
Turbine: a GObject code generator
gnome-c-utils: various scripts
Vim
Tip: to align the parameters on the parenthesis, add (0 to the cinoptions, and use the = command.
The lineup-parameters script from gnome-c-utils (blog post)
GNOME-align-args: plugin similar to lineup-parameters (blog post)