The problem is that most sites for the first two categories are either already taken or politically difficult...
The map on page 25 of
this NREL document
does a good job of showing potential conventional hydropower by state,
separated by already developed, excluded (your political difficulties, mostly), and undeveloped.
There are significant amounts of undeveloped hydro, mostly in the West.
Electricity is, and is likely to remain, a regional thing. The US doesn't have a single power grid; it has three -- Eastern, Western, and Texas -- that are almost completely independent of one another. The Western area is particularly rich in a variety of renewable sources, many located relatively close to the population/demand centers. The Texas area has a more limited set of resources available. The Eastern, particularly compared to its total population and demand, is poor in renewables. In addition, the Eastern's best renewable resources are quite far from the big population centers.