How to express your opinion?

Agreeing:
I tend to agree with you.
That’s a good idea.
I’m with you on that point.
I'll go along with that.
I totally agree with that proposal.
I hold exactly the same view.
I couldn't agree more.
That's just what I was thinking.
That's how I see it too.
That's exactly my position.
 I agree with your point.



Disagreeing:
I see things differently.
I tend to disagree with that idea.
I agree up to a point, however...
You have a point there but...
You could be right, however...
The idea is worth considering but...
Perhaps a weakness of this is that...
Well, I'm not sure of that because...
That might be acceptable if...
I'm afraid I don't agree with you.
I strongly disapprove of the plan.
I'm absolutely against...

Source: http://vocabularyhome.com/general/expressing-opinions-agreeing-and-disagreeing/