SQL Server 2014 Latest CU / Service Pack
For the latest CU and builds (this article will also include service packs when released): 
SQL Server 2014 build versions

As of 2015-01-13, SQL Server 2014 is currently on CU5, which was released Dec. 17, 2014.
Service pack 1 has not yet been released.

Another similar article, specific to Service Packs: 
How to obtain the latest service pack for SQL Server 2014