NEW YORK (Fortune) -- Your business meeting ends early and you're ready to head home - but your flight doesn't leave for a while. It's happened to all of us, and it happened to me just the other week.

I arrived at Chicago's O'Hare Airport a couple hours early for my flight back to New York's LaGuardia. It was a busy Monday and I knew standing-by for an early flight would be tight. But I wasn't flying blind.

That morning, I'd logged into one of my new favorite Web sites, ExpertFlyer. I got an inside peek into the airline's inventory for that day and I knew that the earlier flight at 6:20 p.m. had 14 open seats -- which made my chances for getting on that flight pretty good. (Long story short: I was the last guy who made it on.)

In fact, through ExpertFlyer, I knew almost as much about that flight as the gate agent did.

That's important because on any given flight there are dozens of different fares or classes of service and unlocking them can give you the power to optimize your travel experience.

ExpertFlyer allows you to be your own travel agent (though it doesn't book seats) by helping you find the flights that have better chances for upgrades, or search for the fares that allow much more flexibility without much more dough. (Without this, nailing down frequent-flier tickets or upgrades often requires multiple phone calls, numerous Web searches, and too many compromises.)

Take that same trip back to New York on American. If I were an elite member of American's frequent flyer program and had a flexible schedule, I'd want to see which flights offered the best chance of a free upgrade to first class.

By checking inventory on ExpertFlyer, I could see that the 7:15 p.m. flight has more "X" seats available ("X" is the fare bucket American uses to indicate how many domestic upgrades are available on a particular flight; Delta uses "G"). So before I call my travel agent or go online, I know where things stand. You can even sign up for customized alerts that will notify you if award seats become available on a particular flight.

Another trick is finding coach fares like American's B-fares. They allow the same flexibility of fully refundable coach tickets but are often a couple hundred dollars cheaper. They also allow you to upgrade for 10,000 miles each way, while most coach fares require 25,000 miles and a $250 surcharge.

You can't search this on American's Web site - it will offer you only the cheapest coach seat or the most expensive, full-fare seat, known as a "Y" fare. On a New York to Paris roundtrip trip in August, booking the full fare coach seat cost $3,830 but the B fare on that same flight cost $2,117.

The site, with a starting cost of $4.99 a month, is aimed at travel pros, but a new "consumer version" is on the way this fall. And despite all the site's bells and whistles, I still sat on O'Hare's runway for three hours - sadly, ExpertFlyer doesn't predict thunderstorms.

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Cheat your way to elite status: You don't need to log a million miles to get benefits like express check-in and free upgrades.