Look at EngageNY curriculum (which is really EL Education, Public Consulting Group, Eureka Math, Illustrative Math and a couple of other providers put together). It is pretty excellent, and free! You can also find curriculum from these individual providers separately.

Then, visit OpenUpResources. Same theme.

EdReports.org has curriculum reviewed to align with Common Core.

The above are mostly limited to ELA and Math, for Science, there is OpenSciEd, SCALE/SFUSD Middle School Curriculum, and Mystery Science, for Civics there is Annenberg Classroom, and rest of the social studies, I know some effort is going on, but can't quite remember where the curriculum might be.

The reason I know these is because I run opencurriculum.org (YC W14), and we are trying to bring this information under one roof.