I've just booked a round trip to Paris for $611 on delta/air france, direct flights each way. Had I done it a few months earlier I might have landed a deal just under $500. Keep in mind that fares quoted on web sites are usually over $100 less than what you get after adding taxes and fees. I'm always talking in terms of "final price". This beats the $1300 i'd pay had I booked it in November. Traveling reasonably cheap is all about planning early and flexible dates.
Miles and Frequent Traveler Programs
If you are a regular and/or frequent traveler, you should be enrolled in at least a few mileage programs. I've got United Mileage Plus and Delta Skymiles. Take the time to keep a handy list of which other airlines participate in your mileage program. Here are the Delta Skymiles Partners. Here are the United Mileage Plus Partners. Those partners will come-in handy when hunting for cheap Air Fares.
Lately I've been a great fan of Delta SkyMiles, and here's why: I use the Amex card very heavily to make the most of their Membership Rewards. Those reward points can be transferred to Delta SkyMiles any time. If you do it at the right time of the year (for me, a couple of months ago), you might get some promotional deal where you get an extra 15% on Amex points you transfer to Delta Miles. No matter what you do, strive to link all your billing relationships to something that can eventually translate to miles: credit/charge card, long distance phone, car rental, etc. I've also found delta's web site to be far more usable than united's, as far as their mileage programs go. There's one thing I've also recently discovered on delta skymiles: their partnership with iDine. Now that's a brilliant concept: thru iDine, you create a profile and register a credit card number with them, provided you're like me and crazy enough to trust yet another entity with your credit card info, oh well. Every time you go to a restaurant that participates in the iDine program and pay with the credit card you've registered, you earn SkyMiles. So check this sample use case: Pay for dinner with american express, which gives you Amex reward points, which you could eventually transfer to SkyMiles, but on-top of that, SkyMiles points automagically get credited to your account thru iDine! I had registered for this service a while back ago, but their site seemed buggy, so I never dug further. Last night I look at those mysterious Skymiles credits I received and trace them back to iDine!
Hunting for Fares
Based on fairly flexible traveling plans, you need to look for "deals" in the traveling month you're looking for. Those "deals" are usually not directly surfaced on the front page of any traveling site. It might be one or two clicks away. I've been using Travelocity for a while now, and it's always served me reasonably well. I'm sure there's the same thing on travelzoo.com and expedia, I happen to be familiar with travelocity so they'll be my example. The key is to find a "travel search interface" that lets you pick "flexible dates". That interface should offer you a range of traveling months you can specify.
From that point you should eventually see a list of Air Fares offered by various airlines. Picking the lowest fare at the top of the list is one aspect of the game. Another key aspect is to consider which airlines you have "frequent traveler" relationships with. I won't mind a few extra bucks for a flight that'll earn me miles. I'll also look at direct flights versus connecting flights. On travelocity, try to right-click on the "select" button next to the airline name and select "Open in a new window". Having a specific airline booking interface in a new window allows you to more easily come back to your main list of airlines. A first set of screens will help you pick your "departure date" for the given promotional fare. The following screens will cover the "return date". At the end of this process you should have a clear idea of which specific flights you're hoping to catch.
From this point, you can stay with Travelocity to go thru the entire reservation process. Your other alternative is to go directly to the airline's web site and book those specific flights thru their site. Delta is right now offering 1,000 miles to people who book flights thru their site. My Delta profile happens to also be more up-to-date than the one I have in Travelocity, this tends to make things easier. The flight also came to $10 less on delta's site than on Travelocity's. However, if I remember correctly, Travelocity lets me "hold a reservation for 24 hours" without paying for it, which Delta hasn't allowed me to do.
And yes, I've paid for the flight with the amex card. heh.