Comprehensive Sites
SFUSD OER Math Curriculum, PK-6
http://www.sfusdmath.org/accessing-core-curriculum-unit-plans.html
Utah Education Network Core Lesson Plans
http://www.uen.org/k12educator/corelessonplans.shtml
EngageNY Common Core Curriculum (Select grade and then click on module number)
https://www.engageny.org/common-core-curriculum
Georgia Standards K-5 (Expand grade level on the right hand side to find units for download)
https://www.georgiastandards.org/Georgia-Standards/Pages/Math-K-5.aspx
Virginia Resources
SOL Sample Lessons (searchable database)
http://www.doe.virginia.gov/testing/sol/scope_sequence/mathematics_2009/index.php