National Climatic Data CenterUS and some global focus. Climate Data Online (CDO) provides free access to NCDC's archive of global historical weather and climate data in addition to station history information. These data include quality controlled daily, monthly, seasonal, and yearly measurements of temperature, precipitation, wind, and degree days as well as radar data and 30-year Climate Normals. Includes storm and severe event data for the US.
Good for gathering background data about general weather trends and data over time.