Here are a few things to look for that transmit continuously
TV channels 2 - 6
http://wiki.radioreference.com/index.php/Television
Meteor burst systems
40.53 continuous data SNOTEL in Rockies, Pacific NW
44.20 continuous data nationwide
44.58 nationwide, short rapid data bursts, almost continuous, may have to open up squelch to hear
If you have SSB capability there are lots of ham propagation beacons that transmit continuously in CW between 28.2 - 28.3 and 50.05 - 50.1 MHz
A lot of times the band will be open and many hams won't even know it.
When they eventually figure it out you will start hearing them on
28.3 - 29.0 USB
29.5 - 29.7 FM
Most 10m FM ham repeaters are on these 4 channels
29.62/29.52
29.64/29.54
29.66/29.56
29.68/29.58
29.60 simplex
6m FM 52.525 simplex and repeaters between 51 - 54 MHz
there is a lot of ham SSB between 50.1 - 50.3 with 50.125 USB being the commonly
monitored calling channel.
Also the CB band is a good indicator
http://wiki.radioreference.com/index.php/Citizens_Band
and illegal freebanders mainly between 26 - 28 MHz AM/USB/LSB and even FM sometimes