There is a Hadīth which says that a Muslim govt. cannot ask its residents for any taxes other than Zakāh. On the other hand, we see that our so called Muslim governments seem to be running on the money collected through taxes. Is it religiously binding on us to pay these taxes? If not, then what should be the attitude of a pious person in this regard?

We are bound by the Sharī‘ah to follow and show obedience to the law of the land unless the situation arises in which obeying this law stops us from obeying the Sharī‘ah itself.

In the situation you have referred to, the government is not stopping us from paying Zakāh (in which case one can refuse to obey the directive and face  the consequences as well); it is asking us to comply with its own interpretation of the directives of Zakāh. One group of scholars, it should be borne in mind, hold the view that taxes besides Zakāh can be imposed by an Islamic state. Our duty is to follow the state interpretation in letter and spirit and at the same time, if possible, to convince people in favour of our interpretation in a particular matter. If the majority accepts this view, it  will become the law of the land.

Until such a stage is reached, a person who believes that Zakāh is the only tax a Muslim government can impose on its Muslim citizens can deduct his Zakāh from the amount of tax and pay the balance as Zakāh. If the amount of taxes exceed the Zakāh he is liable to pay, he may not pay any Zakāh.