I guess the same entity that occupies those portions of the West Bank where Israel no longer exerts authority. The Palestinian Authority clearly has the ability to become a recognized nation if it chooses to join the ranks of civilized nations.
It's not willing at present to do so. Unlike Israel's eastern border, there seems to be no dispute as to Gaza's borders, except by those who believe it should be all Israeli territory.
I think those people are crazy, because if it's Israeli territory, Israel just added a million new arabs as citizens.
So something less than a nation occupies those lands. And it serves a lot of political agendas to keep it that way, although it ensures that unrest will continue indefinitely.
A Fatah/Hamas civil war would probably help immensely, assuming Fatah prevailed. There's no chance for a poltical solution between Israel and the sub-nation that occupies those territories to reach any lasting agreement in the present environment.
As a point of interest, there were some adjustments made to the truce lines post 1949. When President Bush alluded to the 1949 lines as valid, the palestinians immediately laid claim to the adjustments which lie in Israel. Of course as I noted earlier, when they speak of occupation, they're talking about Israel. Palestinians speak of Tel Aviv as occupied territory. Fatah and the PLO were attacking to recover that occupied territory prior to the 1967 war.