Katie,
Do read all the boring fine print as you go with Priceline. For one of their air ticket "Express" deals, you aren't selecting a particular flight, but rather a range of time, any major airline, and maybe a stop. Still, when every penny counts, it can work for you.
Flyertalk is one of my most favorite web sites for all sorts of information and advice. Another is
www.betterbidding.com for information about deals on hotels and other travel things.
Romelle
PS - In your first post you mentioned promo codes for the airlines. Those are common for hotels, but the airlines don't seem to use them. However, if you have a trip a ways out in the future, you could use "alerts". These are available on various web sites, and you just code in your particular trip info. Then you get an email if the price happens to drop. New sites doing this crop up, and older ones fall off, but this is a short list of ones that might currently be doing it:
Kayak
FareCompare
Southwest
Yapta (lets one track specific flights)
TripAdvisor
Travelocity
Expedia
Orbitz