The NOAA has hosted DAILY GLOBAL HISTORICAL CLIMATOLOGY NETWORK (GHCN-DAILY) .dat files. Weather.gov has an RSS/XML feed that gives current weather sensor readings. Using the RSS feed as a template, the GHCN-DAILY historical information is used to generate past RSS feed XML documents. The process allows testing on a large set of information with out having to continually monitor the weather.gov site for all the weather details for years.
Detailed GHDN-DAILY information: http://www1.ncdc.noaa.gov/pub/data/ghcn/daily/readme.txt