ORDER BY date or value

Hi Guys!

I’m trying to order my results by a column called start_date. This column can either contain a value such as “Immediate” or a date such as 2012-12-01.

Is there a way I can order my results so that all results containing “Immediate” will come up first, followed by the ones with dates (in date ascending order).

Thanks

ORDER 
    BY CASE WHEN start_date = 'immediate' THEN 'first' ELSE 'last' END
     , start_date