Great info! Don't forget about airlines that offer "Stop Overs" so that you can travel to multiple destinations for the airfare cost of one!
All of these airlines offer that option: WOW, Finnair, Hawaiin Airlines, TAP Portugal, Icelandair, KLM, Air Canada, Etihad Airways, Japan Airlines, Thai Airways, Turkish Airlines and Copa Airlines.
I based a lot of this info on error fares or cheaper tickets, plus I only knew of TAP, Icelandair and Turkish Airlines which offered this service... great to know WOW has it as well! Do you know if there is an exhaustive list to be found somewhere about airlines doing stopovers?