Had booked Delhi - Atlanta return flight for me and my spouse on DELTA.COM for$1894.50. While booking Rail ticket for Kolkatta on IRCTC portal, clicked on the link flight tickets and was pleasantly surprised to find the same itinerary as on DELTA for Rs.94792/ i.e at least$500 cheaper.Thanks to Facebook and Twitter, DELTA responded promptly and offered to cancel my ticket with no charges.I am now booked through IRCTC on DELTA flights.
The layover and flight times are comparable the difference being booking on DELTA.COM the layover is at CDG Paris on both legs and IRCTC the layover is at Heathrow London.
Of the several travel sites and airlines I visited only VIA.COM came close to rates on IRCTC.