Here are some good mediumwave oriented links that I have found on the web. If you have any others you think I should put on the page, let me know!
AM Expanded Band Allotments - The FCC has approved the AM band to be expanded to 1705 khz. Here is a list of stations authorized for that region of spectrum.
Broadcast.com- Broadcast Network of the Internet. Listen to radio stations and watch video from all over the world with Realaudio.
Switchboard - OK, it's not really a radio site, but it's a great place to find addresses, phone numbers, and FAX numbers of US radio stations.
Infospace - Online telephone directory similar to Switchboard.