The first map presented is the most recently made. There are 2 maps: Shelters (the Relief Map) and requests for rescue (the Rescue Map). The Relief map is created from people mapping requests for help on social media using the #HarveyRelief tag and is updated in real time. The map is powered by volunteers. To learn how to help, click on the "Menu" in the upper left.
The Washington Post made a series of maps to accompany its news reporting, starting from prior to it reaching landfall that showed predicted rainfall, population density, flash flood risk, petroleum infrastructure. They have also created nice maps showing total rainfall and stream gauges (indicating if they are rising or falling).
As usual, the New York Times has some excellent map-based infographics, showing the storms past and predicted path, numbers and locations of evacuees, extent of flooding, rainfall maps, which rivers have flooded, and the height of the crest, and past hurricanes in the Texas Gulf Coast region. In addition, they tweeted a nice animated map showing rainfall totals.
Esri created a story map titled "Hurricanes and Tropical Storms Overview" that can be used to track storms in all the major hurricane/cyclone regions, but is focused on Hurricane Harvey and its remnants. On various tabs, you can see precipitation forecasts, and a map of area impacted by the storm surge.
There are many more excellent maps out there, but the last one featured here is from the Gulf Restoration Network, showing the huge number of low-lying contamination environmental risks in the Houston-Gulf Coast region.