In my recent work, I have been exploring The OER Commons website, which is a digital library and network of Open Educational Resources. It allows you to search, with a search feature that really lets you refine down to exactly what you are looking for - whether that be full lesson plans, videos, full units of study, online courses, etc. You can also review and comment on resources, which is a nice feedback feature that allows for others to gain from those who have used a resource. You can create your own content to share or link to others and collaborate.
Once you narrowed down the search, you can look at your results, click on them for more
Again, there are many places to go to find OER but I like what I have explored so far on the OER Commons website, in particular the ability to find Common Core Aligned lessons, resources and educator support. Worth exploring.