Geek Feminism’s Wiki contains all kinds of goodness. Although it’s no longer being actively maintained, its content a remains solid, evergreen resource for all things inclusion, from an intersectional feminist lens. Jump straight to the best Code of Conduct starting point here.
WoC in Tech Chat released their image collection of women of colour in the workplace on flickr in 2016, and have been a trusted resource of beautiful, inclusive images ever since. Be sure to attribute them as per their Creative Commons license.
Broadly recently released the Gender Spectrum Collection, a beautiful collection of images that show trans and non-binary folks in real-world scenarios, outside of typical clichés and stereotypes. Note that these images cannot be used for commercial purposes (so, these can be used in the context of open source projects and developer blogs, but not on company websites), and please be sure to read these guidelines completely in order to use these images mindfully.
The Gender Decoder is a simple writing tool that is typically used to optimize the hiring experience, but can be used to vet any human-facing content in American English. Based on linguistic research, the Gender Decoder will output tactical feedback on word selection and propose alternatives to make your content more welcoming and inclusive. The project can also be found on Github.
Code of Conduct enforcement training is crucial to ensure you can respond to any code of conduct infractions. Valerie Aurora and Mary Gardiner have written a fantastic (and free) code of conduct enforcement book that can be downloaded here.