Icelandair has some falls sale fares from Boston, New York and Seattle kicking in to various European destinations. A round trip between Boston and London, for example, costs $626 with taxes and fees included.
The fares are available from Boston for flights between Nov. 1 and Dec. 10; New York , Nov. 15 to Dec 16 ; and Seattle, Oct. 25 to Dec 16 . Technically this is indeed a fall sale, but it seems more of a pre-winter sale to me. Brrr.