to agree we can use the following expressions.

neutral:
yes, l agree,
true enough,
that's qiute right.
l couldn't agree more,
informal:
yes,
right,
dead right,
well that's the thing
you're right,
l'm with you there,
formal:
l agree entirely
l'm of exactlythe same opinion.
TO DISAGREE we can use the following the expressions.
neutral:
l dont agree
l cant agree
not realy
l dont think that's right.
informal:
no way.
never!
never!
nonsense!
you cant be serious!
 you must be joking.
formal:
l entirely disagree...
l cant accept...