If you don't know what Twitter is, then read this.
If you do know, but you aren't following the airlines' discounted fare feeds on Twitter, then you're missing out on some very low fares--fares that you can't find anywhere but Twitter (btw, we do list Twitter fares when we see them).
Here are links to the airlines' Twitter feeds. Not all are using this channel to direct market low airfares to consumers. In fact, so far we've only seen United and JetBlue do it. Interesting that JetBlue has two Twitter accounts (a general account with over 1 million "followers," the other its "Cheeps" account, linked below, which is where you'll find the fares tweeted).
JetBlue
United
Southwest
American
Delta