I thought this would be an easy one but had to get some help too. Try this...

declare @dt table ( akey int, d1 datetime, d2 datetime, d3 datetime )

insert into @dt values (1, '2012-01-01', getdate(), '2012-09-01' )

insert into @dt values (2, getdate(), '2012-01-01', '2012-09-01' )

insert into @dt values (3, '2012-01-01', '2012-09-01', getdate() )

select

akey, max(dates)

from

( select akey, d1, d2, d3 from @dt ) p

unpivot (

dates for datevals in ( d1, d2, d3 )

)

AS unpvt

group by akey