What are some research resources that you have found particularly helpful?

By michel @ 2021-10-06T16:00 (+7)

I am helping Effective Thesis try to improve their Resources page. For any of you involved in research, it would be great to crowdsource valuable resources or pieces of advice you wish you had found or learned earlier. These might be:

The existing content is already solid (check it out if you haven't already!) but I'm sure there's more out there. Feel free to link me to similar questions/discussions that I may have missed.