List of SharePoint Security Updates

TechNet has a great resource located on their Microsoft Security Bulletins page to list all of the security updates for all products, including SharePoint Server.  To see the list of updates, go here, then under Search by Product or Component, select the appropriate version of SharePoint, then click the Search by Product or Component button.  It will list all applicable security updates below.   And of course, standard SharePoint updates can be found in the TechNet SharePoint Update Center for SharePoint 2010 and SharePoint 2013.