These are websites I personally find useful and refer to a great deal:
Access to Insight (translations of the Pali Canon, the closest we have to original Buddhist teachings)
Antaiji Temple (a traditional training temple in Japan)
The Buddhist Society (UK)
Chocobuda (Spanish language website of my dharma brother and teacher Kyonin Barros)
Everyday Zen (with a very useful collection of Zen study resources)
Lion’s Roar Buddhist Magazine
Rising Lotus Zen (an online sangha led by Jill Kyoji Freeman and Daishin)
Sokukoji (Michigan, USA)
Sotoshu (the head organisation of Sōtō Zen Buddhism)
Sōtō Zen group (Facebook)
Treeleaf Zendo (my online Zen home)
Tricycle Buddhist Magazine
Upaya Zen Center (Santa Fe, USA)
Zen Mountain Monastery (NY, USA)
The Zen Site (a serious amount of resources here!)
Zen Studies Podcast (a very useful way to systematically learn about Sōtō Zen)