Let me demarcate the rough boundaries of the Harappan Civilisation.
The core: The core area of the civilisation was the Mohanjodaro-Bahawalpur-Harappa triangle. Therefore, maximum sites are found in this area.
Peripheries: Since Harappan civilisation was essentially urban in character, this meant the need for procurement of resources from different sites and also distribution of various materials to its cities and settlements existed. Therefore you can find sites in the rough terrain of Makran Coast, Afghanistan, Kashmir and even the Ganga-Yamuna Doab.
However, to give you an idea of the extent, lets mark the northern, eastern, southern and western boundaries.
Now let’s get to the settlements. There are a lot of settlements, the listing of which, will be a redundant task. I would refer you to this wiki page: List of Indus Valley Civilization sites
Remember, there are a lot of un-excavated sites. And it is possible there are many sites which lie under the present level of occupation, undetected.