The grammatically correct one is
I want two other methods.
This implies that the two other methods, combined with the original method, are not the only appropriate methods. The asker is thinking that the methods you already told him/her about aren't adequate enough, and wants two more methods.
"other" should have some modifier or quantifier or the definite article preceding it, so your second sentence is ungrammatical.
I want the other two methods.
This means two (contradictory!) things:
that the person wants the other two methods out of some total amount.
that the person doesn't want your currently selected method, but rather he/she wants the other two methods out of those total.
You'll have to tell which is which by context.
To go off-topic:
I want every other thing.
Come back some other time.
I hate that other car.