These radar sites are some of my favorites.
Local Radar: This page, run by the NWS shows basic radar for different areas across the country. For interactive radar, head on over to our home page where you will find a great interactive radar resource.
E-wall radar: This webpage, run by Penn State is an extraordinarily complex collection of data but their radar resource is excellent. It offers a 6 hour loop of one of 5 regions listed to the left (sorry residents of the south-central US, they do not have a radar loop for you...). It shows precipitation-type (rain, snow, mix) as well.
Advanced Radar Options: This webpage run by weatherunderground offers a cruder basic radar as well as an array of more advanced radar options such as echo tops, total rainfall, velocity products and lots more. Good for those who live, think, speak weather.