links to archived data
surface analysis:
http://www.wpc.ncep.noaa.gov/html/sfc-zoom.php
http://www.wpc.ncep.noaa.gov/archives/web_pages/sfc/sfc_archive.php
soundings:
http://www.spc.noaa.gov/exper/soundings/
http://www.spc.noaa.gov/exper/soundingclimo/
SPC mesoanalysis/severe events archive: (tons of maps: radar, satellite, surface, upper air, parameters for severe weather)
http://www.spc.noaa.gov/exper/ma_archive/
http://www.spc.noaa.gov/exper/archive/events/
NCAR image archive: