Good news, Lync 2013 Server RTM bits, along with Exchange 2013 and SharePoint 2013 are now on Technet and MSDN, Office 2013 with the Lync 2013 client is also on TechNet MSDN,
In addition the RTM help file, Visio Shapes and Unified Communications Managed API (UCMA) 4.0 are all available. All that you need to get started with 2013!
Lync 2013 RTM Documentation:
Lync 2013 Visio Shapes (updated link, all office server 2013 shapes):
Unified Communications Managed API (UCMA) 4.0 (for application development):
Lync 2013 Best Practice Analyser:
Exchange 2013 RTM Documentation: