www.craftbeerradio.com - Craft Beer Radio has a large number of broadcasts archived for download or streaming audio. They are very informative and enjoyable and they do a lot of shows on local breweries. I highly recomend you check them out.
www.beerradio.com - Beer radio can not only be listened to online, they have a weekly broadcast on sirius radio. They also have a rss feed and podcasts available on iTunes.
www.thebrewingnetwork.com - The Brewing Network seems to have been around the longest and seem to be the most in depth online beer radio show out there. They have four different shows that are available for download and the archives for each show seem to go back quite a ways. The shows are: the Sunday session(the one that started it all), the Jamil Show that covers brewing classic styles of beer, Brew Strong which covers cutting edge beer and brewing news and Lunch Meet, which doesn't seem to be about beer at all.
http://goodbeershow.com/ - The Good Beer show is less radio and more video, so for all you visual people out there, this beer show is for you!
http://pacificbrewnews.libsyn.com/ - Pacific Brew News is a show very near and dear to my heart. While their podcasts may cover beers that are not readily available here, there is some great information. On top of that, there are a few that get distributed here or you can order them from http://www.liquidgratitude.com/Default.aspx.
http://www.citizen-times.com/apps/pbcs.dll/section?Category=PODCASTS02 - The Beer Guy Tony Kiss from the Asheville Citizen times has an online podcast you should check out. There is a new show every Wednesday and each episode lasts about 20 minutes.
So that should get you started. As I find new shows that look interesting, I will add them. If you come across one that you think should be posted, just add a comment. Happy drinking and listening.