S.A.M.E., All-Hazards, and Public Alert are the buzzwords to watch for. S.A.M.E. stands for Specific Alert Message Encoding and is a versatile system that allows you to choose exactly what kinds of alerts you want to hear, and even when to hear them.
I have a couple of the Midland WR-300 models around the house, and one in each vehicle and I'm quite pleased with them.
This link gives a pretty good amount of information on the Public Alert system: http://www.nws.noaa.gov/nwr/nwrrcvr.htm(edit: fixed typo in model #)