Across the radio spectrum, there are a whole heap of interesting frequencies where you will find activity. Over time I plan to slowly compile a list of things to listen for.

20m Band (14Mhz)
  14.070    Digital Modes (Mainly PSK31)
  14.076    20m JT65 Calling Freq
  14.230    SSTV Calling Freq
  14.236    FreeDV Calling Freq