Join Date: Apr 2009
Location: Bye Delta
Programs: AA EXP, UA Silver, HH Diamond, IHG Plat, Hyatt Plat, Marriott Titanium, Nat'l EE, Avis PC, Hertz PC
Posts: 16,635
Best one I ever found myself was BOS-SAN on United, $10 base / $30 AI one-way in March 2011. Route through IAH for $0.0105 per EQM, and this was back when RDMs were distance based, so nearly $0.005 per RDM if you were elite and earning a 100% bonus. Didn't book, as I live in the midwest, but plenty on the MR forums booked it and it was honored.
Best one I didn't find, but was able to book myself, was Delta's mass mistake fare fiasco of 12/26/2013. ORD-LAX for under $5 base, $28 all-in one-way. Route via ATL for maximum miles, again about $0.011 per MQM and $0.0055 per RDM. I believe they had a bunch of premium fares that were bungled also, but I didn't book any of those.