Jeff:

Check http://www.primetimeshortwave.com/ for a comprehensive schedule (based on UTC, coordinated universal time).

Try WWV and WWVH:
5000 / 10000 / 15000 / 20000 khz. Lower frequencies at night, higher frequencies during the day.

Next I'd recommend learning what the broadcast bands are, and try scanning through them. On this Wikipedia page, see the section labeled ITU Frequency Allocation: http://en.wikipedia.org/wiki/Shortwave

Good luck and let us know what you find. I'm also curious about which radio you have.