The National Solar Radiation Database offers solar radiation data and limited meteorological data for 237 sites in the US over the period 1961-1990, and expanded data for 1454 sites from 1991-2005:

Data includes:
Hourly Solar Data
Statistical Summaries
- Daily Statistics Files
- Hourly Statistics
- Threshold Files
Solar Radiation Data Manual for Buildings
Solar Radiation Data Manual for Flat-Plate and Concentrating Collectors
Typical Meteorological Year (TMY2) Files
User manuals in PDF format can be downloaded. Data is in text format, but can be converted to spreadsheet format with a bit of work.
Via Treehugger.
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- The Geonames.org Geocoding Database