Summer 16 introduces two new methods that (finally) eliminate the clever hack by @pjcarly:

For VF, HTML, and Plain Text templates:

Messaging.SingleEmailMessage email = 
            Messaging.renderStoredEmailTemplate(templateId, whoId, whatId);

To get just the merged results from the templateBody (and any errors)

List<Messaging.RenderEmailTemplateBodyResult> resList = 
        Messaging.renderEmailTemplate(String whoId, String whatId, List<String> bodies)

where bodies is a list of strings corresponding to the value of EmailTemplate.body as queried from the database

String[] bodies= [select body from EmailTemplate where developerName IN ('foo','bar')]; 

Summer 16 introduces two new methods that (finally) eliminate the clever hack by @pjcarly:

For VF, HTML, and Plain Text templates:

Messaging.SingleEmailMessage email = 
            Messaging.renderStoredEmailTemplate(templateId, whoId, whatId);

To get just the merged results from the templateBody (and any errors)

List<Messaging.RenderEmailTemplateBodyResult> resList = 
        Messaging.renderEmailTemplate(String whoId, String whatId, List<String> bodies)

where bodies is a list of strings corresponding to the value of EmailTemplate.body as queried from the database

for (EmailTemplate et: [select Body from EmailTemplate where DeveloperName IN ('foo','bar')])
  bodies.add(et.Body);