For me it was this one...

http://www.flyertalk.com/forum/showthread.php?t=122417 back in 1999.

I flew about 300,000 miles that year and earned hundreds of thousands of Hilton points. I've never been a huge customer of Hilton, but I have been enjoying free stays (roughly one or two per year) for nearly a decade at Hilton's, thanks initially to reading this thread. Here we are now, 9 years after that thread was posted and I still have 100,000 Hilton points in my account. Maybe half of those points are left from this promo, and the rest are from a handful of paid Hilton stays over the years.

On top of that, thanks to another Flyertalk thread on Amex Centurion, I get comped to Hilton Gold each year so when I do take a free Hilton stay somewhere, I get free Club access and upgrade!

So how much is 9 years worth of quality free Hilton stays worth? Thank you Flyertalk!! ^

in my case it was the conrad bangkok mistake.

the 'highest gain' is subjective in this case...my gain was not so much because i got to stay in the presidential suite at the conrad in bangkok--which was fabulous, mind you--but because getting in on that deal was the moment that mr kk decided that my little hobby was NOT weird after all, and was in fact a very good thing for me to be doing. once he was on board, all the miles and points stuff got easier...and i've been 1k ever since, with mr kk supported mileage runs. that's entirely due to his getting to stay at the conrad...which goes back to that thread. ^

Fare mistake deals to Fiji ($61 incl tax) and Iceland ($55 incl tax) as well as earning 1.2 million miles from referral programs when I published the now-defunct Mileage Workshop website.

I was pretty excited about getting 15k Delta miles through the recent Avis promotion. Clearly I can set my sights higher. ^

The US $2 Lebanon, NH and Watertown, NY fare. ^

This recent UA C misprice to AKL probably my best haul as the $1500 spent not only got me upper deck biz class SFO-SYD-AKL and I'd never visited AKL so it was a destination I was keen on seen but it also made me elite for the first time on any airline ever plus I banked approx 25K UA MP miles which was worth approx. $600 when I redeemed an award ticket YEG-ORD recently. All in all not a bad haul in my books. ^

Small potatoes compared with others but I actually like small potatoes.

Probably the "Fly Concorde for $1100" which made its debut in 2002. Buy a few magazine subs from Randy, obtain SPG * points, convert them to QF miles at a 1:2 ratio, use QF miles to purchase an F fare (usable on Concorde) from NYC to LHR on BA!!! $1100 later, you've been on Speedbird!

Dave

The good old goldpoints - magazines.com - deal.

I think I got about 50 or 60k miles on that one just ordering magazines I read anyway, plus giving some as gifts.

I believe there were some people ordering subcriptions and giving them as gifts to hospitals/charities. They earned alot of points

And lets not forget the free hotel night offers for credit card sign ups.
Not to mention free airline miles for cc sign ups.

And lets not forget the $250 credit promos when you spend at least $..... on your new credit card.

These aren't the highest gainers for me, but collectively they add up.

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Seats available.

FTers more than a specific thread - RichLond, Darren, Guy Betsy and 2 Many Miles teaching me how to construct OneWorld RTW trips. I got 36 segment 6 continent tickets out of Sweden, then out of South Africa, for amazingly affordable prices ($3.5K if memory serves me correctly). My husband and I traveled comfortably to places like Easter Island, Capetown, and St Petersburg, places that weren't even in our radar screen before learning about these tickets. These were awesome awesome deals, sadly now gone with the OneWorld tickets capped at 16 segments at a substantially higher price.

Those were winners for me...dirt cheap summertime fares and I got to spend weekends in places like Montreal and coastal Maine.

There was also a post-SARS mistake fare on CX from SFO to places like SIN, MNL, and BKK. I flew to Koh Samui for about $250 all in and stayed in a fantastic suite at the old Royal Meredien for under $100/night.

The BA $20 fare mistake.

That was my discovery {taking a bow} thank you, thank you very much....thank you.

For me, off the top of my head...

*Obviously, AKL in C for $1500 a year ago
*Fast Track to Gold & 50,000 point bonuses at Hilton in 2000- before the point devaluation. I racked up 200,000 in 3 weeks at the SFO Airport HHonors hotels.

The good 'ol promo codes on US back in 2000/2001!!! Anyone else remember the Getting Out Miles??? I'm so glad I was in the " Club" for that one! I think alot of US flyers were hitting a Half Mil in a few months of flying

I think I took a flight to CDG and FRA (in Envoy natch), as well as a ATL-CLT-SAV-CLT-ATL trip and racked up about 175,000 miles.

That, along with their Early Paper Upgrade Certificate trade-in for miles (when they went electronic) saw my Dividend Miles balance hit a nice number!

Best one to date was this one...
All in, I bought 3 tickets from Chicago for about $500 each and managed to snag 57,973 EQMs and RDMs for absolutely nothing. Air Canada simply canceled the tickets, but issued miles as if they had been flown, so in the end I was almost content, but I still wanted to try out all the different airlines I had tickets on.

One thing I will say that I am most thankful for learning from FlyerTalk was about the whole concept of MRing. I used to spend $30k a month on my Amex when they had double points to try to earn free airline tickets, but now all I have to do is simply book a few MRs and some nice vacations and it all pays off.