Most of our friends and family know that we like to travel, and that we don't like spending a ton of money to do so. The Boarding Area has a great blog post today that explains a little bit about jumping on "mistake fares", and I'd strongly suggest reading it if you're interested in scoring a ticket to an exotic location for less than you'll often pay to fly domestically.
It's important to note that if you're the kind of person who wants to visit a specific city on a specific weekend, or you need a week to "think about it" before booking an international trip, you might as well not even bother. The keys to scoring these deals are to notice them when they happen (I follow some key Twitter accounts that tend to broadcast them, such as The Flight Deal, which is mentioned in the article) and booking them immediately, often within an hour or two of them being found. Many of the airlines will let you cancel a fare for free within the first 24 hours, so book the trip first, then ask your boss for the time off!
Often these cheap fares tend to be for travel in the winter or shoulder seasons, but we've found that the lack of crowds often makes up for slightly cooler weather.
Here are a few examples of crazy cheap sales and/or mistake fares that we've flown, all were round trip:
Chicago to London for $221
London to Florence for $16
Chicago to Paris for $250
Chicago to Johannesburg, South Africa for $390
Chicago to Beijing for $528
Minneapolis to Copenhagen for $351
Other Twitter accounts to follow:
AirFare Watchdog (Consider signing up to receive a daily email from their site showing you the fares that are on sale from your home airport as well)