Contents
Best Practices
https://technet.microsoft.com/en-us/library/cc778219(WS.10).aspx
Active Directory Best Practices (PDF)
AD Deep Dive
This is a very in depth document on AD Design. Worth the read, just don't do it in bed because it'll put you to sleep.
https://technet.microsoft.com/en-us/library/bb727085.aspx
Best Practice Active Directory Design for Managing Windows Networks (PDF)
TechNet: Designing OU Structures that Work
https://technet.microsoft.com/en-us/magazine/2008.05.oudesign.aspx
Active Directory Structure Guidelines
I find these articles very useful whenever I consider designing or overhauling an AD OU structure.
http://www.grouppolicy.biz/2010/07/best-practice-active-directory-structure-guidelines-part-1/
http://www.grouppolicy.biz/2010/07/best-practice-group-policy-design-guidelines-part-2/
2008 R2
https://araihan.wordpress.com/2011/05/28/microsoft-active-directory-best-practice/
https://araihan.wordpress.com/2012/07/29/microsoft-active-directory-best-practice-part-ii/