To get a good overview of third party libraries 'out there', you can browse the index at http://godoc.org/-/index

These are by no means all the 3rd party stuff out there, but it's a good starting point.

Incidentally, this website is intended to automatically generate and serve the documentation for all those projects in a centralized place. You don't even have to submit your projects. Just type the import path in the search box, and the site fetches the code by itself.

Edit: And here's anther community-built site to do continuous integration testing for your projects. It too, has an index of registered projects: http://goci.me/