Intellicast NEXRAD Data - National USA radar image, map. Updates twice per hour. Links to other radar maps: Summary, Regional, Local NexRad, Storm Relative Mean Radial Velocity.
Live Weather Images - NEXRAD images directly from the National Weather Service covering the United States.
Plymouth State College NIDS Data - Free and regularly updated NEXRAD radar data. All NEXRAD sites are available on the site and several radar modes are offered as well including Base and Composite Reflectivity, Base and SRM Radial Velocity, VIL, and Storm Total Precipitation.
WeatherMatrix Radar Supersite - The WeatherMatrix organization, formerly CASI, has put together a nice collection of radar-related links. The links range from those to current radar data, to links about radar sites and how they work. StormMatrix, a very unique feature to the Internet, is the only place you can find free NEXRAD storm table data online(30 min delay).
WeatherTAP - Commercial site offering NexRad Doppler Radar maps, updated every 6 minutes, including national, regional and state radar maps, and lightning strike data.
