BetterLesson is a site that has a large number of lesson plans, presentations, resources, unit plans, curricula, and more from other educators. You can also upload your resources to share with others.
The site also allows users to comment and converse about the different resources. The resources are searchable and are sorted by grade level and subject. There are a lot of great resources on here.
It is free, but you do need to use your email address to sign up and then you create your account. This allows you to upload content and also "bookmark" resources to use later.