American Airlines

American Airlines had their hub in DFW (Dallas FortWorth). They had a software company called Sabre that handled a lot of their logistics, databases, time management, time tracking software etc and they would also sell and customize the software for other airlines.
Since UTA had a good computer science department, a lot of graduating students would get jobs at Sabre.
Sabre had great benefits for their employees (D1 tickets, where they could fly anywhere in the US for free if there were empty seats) and friends (D3 tickets, where you could fly anywhere in the US for 60$ a flight!!!) and family (D2 tickets, where you could fly for free anywhere in the US if seats were available).
Naani/ Kiran/ Kishore and a bunch of other seniors of mine worked at Sabre and enjoyed these benefits greatly and were kind enough to share the D3s with me now and then.
The funniest incident was when Vidya gradauted and was moving from UTA to Chicago to work for Motorola, we had 3 cars (Vijays, Naanis and Naresh's cars) go to the airport to drop her off at the airport, along with a bunch of us who were going to see Vidya off. She was on the 3pm flight.
There were empty seats in the flight, so Naani, Kiran, Kishore, and Prathiba all decided to fly to Chicago to see Vidya off! Naani left his car in the airport and they were off to Chicago!
They came back late that night, brought back Naani's car and came back home!
50$ to England, 35$ to south america etc were some of the fantastic fares that were offered and used by the folks at Sabre.
I visited my family in Pittsburgh a couple of times using D3s and flew to a couple of other places as well.
When the software industry had a recession in 2000, D3s and D2s were withdrawn and they had restrictions on D1s as well.

American Airlines, still had good deals with their NetSAAver emails on Tuesday morning. Fly out on a Friday or Saturday and come back on a Sunday or a Monday to some places for 99$. There would be a limited number of seats. You had to register your email ID with AA and they would send out an email Tuesday mornings @ 6 and the tickets would be sold out most times before noon.

We flew to Missouri/ Colorado/ New Mexico/ Pittsburgh and Boston on these fantastic NetSAAver deals.

As DFW was the hub, most times I flew AA since there was better deals and connectivity and ended up racking up quite a few miles (travelled some 8 times in 2004 and 12 times in 2005 for work along with several personal trips). In 2006, before moving back, we used up all our miles and got 2 free tickets to see family in Pittsburgh.