I'm not sure how long they will last, but I saw an ad a few days ago promoting Southwest Airlines' new Oakland-Denver service and fare sales. Checking dates for a typical Worldcon trip for me (in the day before, out the day after), I found fares of $99 each way before taxes ($219 net). The best fare for the same dates I could coax out of United's web site was $375 net. Now, I'm planning on driving, which will almost certainly be more expensive (even factoring in that it's two people), but if you're planning on flying, you might want to check out this fare before it fills. And as far as I know, Southwest hasn't (yet) adopted United's tightwad baggage policy.