Microsoft Dynamics CRM 2013 Service Pack 1 (SP1) is now available.
(Referred to as CRM Online Spring ’14 Update in Microsoft Dynamics CRM Online)

The build number for this release is 6.1.0000.0581

New features in this release include:

• Microsoft Dynamics Marketing – Plan, drive and measure marketing
  
• Microsoft Social Listening – Social media and sentiment monitoring
• Improved Customer Care – SLA Management, Entitlements and more
  
• Enhanced Mobility – Support for Windows 8.1 and improved Android and iOS apps.
  

Important Microsoft Dynamics CRM 2013 SP1 includes all updates that are contained in Microsoft Dynamics CRM 2013 Update Rollup 2 and also contains new updates. CRM 2013 SP1 will be required for any future update rollups that are based on CRM 2013 SP1.

Useful Links

Microsoft CRM Spring 14 Release Preview Guide
Microsoft Dynamics CRM Customer Centre – Get ready for the next release
Microsoft Dynamics CRM Readme
TechNet Article – Update Microsoft Dynamics CRM 2013
Download – Microsoft Dynamics CRM 2013 SP1