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.