I (totally) agree with you / that.

我完全同意。

I couldn't agree more.

我再同意不过了。

I'd go along with that.

我会赞同的。

I feel the same.

我有同样的感觉。

You're absolutely right.

你绝对是正确的。

Absolutely / Definitely / Exactly.

绝对是。

No doubt about it.

毫无疑问。

That's a good point. / I see your point.

这是一个很好的观点。/我明白你的意思。

I see where you're coming from.

我明白你的观点。