I don't know any codes, but what I've been doing is checking Bestfares.com twice daily under their Quick Fares menu. I usually check in the morning and again about 5:00pm. It gives me rates for nearby airports also. Then, I go to travelocity to see who the carrier is, since Bestfares only shows rates for the 'members only' section. I can usually find the same rate (within $10) on travelocity. So far, I haven't been able to use any of the deals as my trip isn't until end of Sept and no one is posting schedules that far in advance for deals. What I plan to do though, is to contact the airline directly because you can often get an even better deal than what is published on other sites.
I hope this helps you!
Good luck!
Anna