Latest geostationary weather satellite imagery in visible, infrared, or water vapor: http://www.rap.ucar.edu/weather/satellite (NC closeup available)

GOES Project Science (imagery, movies, animation, tutorials, historic events, etc.): http://rsd.gsfc.nasa.gov/goes/

Selection of latest imagery around the globe (GOES-GMS-METEOSAT): http://www.nrlmry.navy.mil/sat_products.html or: http://www.goes.noaa.gov

GOES Gallery of significant weather events: http://cimss.ssec.wisc.edu/goes/misc/

Satellite observed global sea-surface temperatures (SST): http://www.osdpd.noaa.gov/PSB/EPS/SST/climo.html

Latest "Space Weather" (aurora, solar storm activity): http://www.sec.noaa.gov/

Other sites for exploring satellite imagery:

Colorado State University "RAMSDIS:"
http://www.cira.colostate.edu/RAMM/Rmsdsol/main.html

University of Michigan "WeatherNet:"
http://cirrus.sprl.umich.edu/wxnet/radsat.html

National Weather Service - Storm Prediction Center "Past Cool Images"
http://www.spc.noaa.gov/coolimg/