NASA
Global Hydrology and Climate Center
Has information and hydrology data from around the world. It also has a section discussing human impacts on the climate and another which covers current research.
NOAA
Noaa: Nws: Office of Hydrologic Development
Has general hydrology information, hydrology research updates, and data from the National Remote Sensing Center. A good site discussing current information from the world of hydrology.
US Geological Survey
U.s. Geological Survey: Drought
General information about droughts includes how to determine when a drought begins and what areas of the United States they are most likely to occur.