I've been on an awesome run of trips recently. I've gone to China, Peru, Mexico, and Japan, and have paid $1350 total for all four flights. That's roughly the cost of the normal price of just ONE of the more expensive flights on that list. I have a few tricks to share with you which are responsible for these four flights.
FlyerTalk Mileage Run Forums
You may already be aware that there's a group of people online who are completely obsessed with miles and status on airline frequent flyer programs. They all congregate on a site called FlyerTalk.com and discuss mileage runs, which are flights so cheap that it's (nearly) worth going just for the miles. In fact, many members go on trips that last for just hours before they get back on the plane home.
You may not want to take trips like that, but you can use their forum to find extremely cheap flights (and get miles while you're at it). Just go to the Mileage Run subforum and search for your home airport. You can also check out this thread which has deals that are still very cheap but don't earn enough miles to qualify as a mileage run. Sometimes that's because the price is a bit higher, but often it's because it's an obscure airline with a crappy frequent flyer program or a fare class that doesn't offer miles.
This is where I found my Mexico flight, which was $273 for SFO-CUN. It also earned me ~$50 worth of frequent flyer miles.
GetGoing is probably my favorite new startup, despite the fact that they got into Y Combinator and I didn't. The premise is that they have very low fares, but you can't choose exactly which one you want. Instead you pick two that you're willing to go on, put in your credit card info, and then randomly get booked on one of the two.
I chose Shanghai for $480 and Beijing for $500, which are both excellent prices. I was lucky to get Shanghai, which I had a slight preference for.
Good fares are somewhat inconsistent, so make sure to add everywhere you'd like to go as a favorite so that you can look at all possible options. On the West Coast they always seem to have great deals to Hawaii (~$250), so if there's only one great foreign fare, you can use Hawaii as a backup.
Another trick is that if you link your Facebook account with them, you get $25 off your first flight. That would have dropped my China trip down to $455 if they were running the promo back then. And if you refer friends (as I'm doing here), you get $50 if they book a flight within 90 days.
Kayak Price Alerts
I learned this trick from my friend Jenna Meister, who found both the Peru ($284) and Japan ($315) flights. Very occasionally, airlines will have ridiculously low fares for very short amounts of time. If you set up alerts properly in Kayak, you can get emailed whenever something good comes along.
To set these up, go to kayak.com/alerts and click "Add a flight price alert". Click "Top 25 Cities" and enter in your home airport and the region that you're interested in. Fill out your max price, switch the frequency to daily, and hit Save. If you want to go to a specific airport that's not a major hub, you could also add a fare alert for that specific city pair. Besides SFO, I also add OAK, SJC, LAX, and LAS as separate alerts, since it's very cheap for me to get to any of those airports.
You should now get emails occasionally when these deals pop up. It's important to jump on them VERY quickly. Often they evaporate within a few hours if not minutes. You can also check from the Android or iPhone apps throughout the day. I'm not too experienced with this, but Jenna recommends it.
Most importantly-- if you find a good deal out of one of my airports, email me and tell me about it! Dinner's on me if I book it!
Photo is from Gangnam, Seoul. Yeah, I did the dance.