T-SQL (SS2K8) :: Finding Maximum Value Out Of 5 Different Columns?

How can we find maximum value on column level? Suppose we have table A with four columns col1,col2,col3,col4, Now my query look likes this:

Select col1, col2,col3,col4,
(col1 + col2) as addcol1,
(col2 + col3) as addcol2,
(col3 + col4) as addcol3,
Max(addcol1,addcol2,addcol3) as maxvalue
from Table A

I am getting error as max accepts one argument, I cannot use case statement as table is already bulky and it will make my query more expensive.