SQL Server 2008 usando COUNT() OVER
select *, c = count(1) over (partition by zip)
from tbl
order by c desc;
Si no necesita ver la columna adicional, puede mover COUNT() OVER
cláusula en la cláusula ORDER BY.
select JobCode, Job1, Job2, Job3, zip
from tbl
order by count(1) over (partition by zip) desc;