The winter fare sale started last weekend is still going strong from Chicago ORD with fares to Amsterdam, Brussels and Paris in the $400s and Frankfurt at $507 roundtrip for departures early December and from about January 11 to March 31. Icelandair has even lower fares and lowest fares of all are generally Star Alliance fares found through Momondo.com searches at online travel agencies.
All links below show Google Flights fares for Sat Feb 11-Sun Feb 19 and mostly match lowest fare shown.
Amsterdam
Star Alliance $439-$454 Dec 9-20; Jan 10-March 31
SkyTeam $439-$454 Dec 9-20; Jan 10-March 31
Oneworld $454-$485 Dec 9-20; Jan 11-March 31
Brussels
Star Alliance $443-$483 Dec 10-20; $443 Jan 11-March 31
SkyTeam $458-$493 Jan 10 – March 30; $468-$528 Dec 9-19
Oneworld $476-$515 Dec 10-14; Jan 11-March 31
Frankfurt
Star Alliance $507 Dec 9-20; Jan 11-March 31
Oneworld $519 Dec 10-16; Jan 11-March 30
SkyTeam $522 Dec 9-19; Jan 11-March 31
Paris
Oneworld $472-$484 Dec 9-20; Jan 11-March 31
SkyTeam $472-$487 Dec 9-20; Jan 11-March 31
Star Alliance $471-$476 Dec 9-20; Jan 11-March 31
American Airlines Chicago ORD – Paris CDG (AA nonstop) – Helsinki HEL (Finnair) – Chicago (Finnair)
$471.96 round trip Friday March 31 – Sunday April 9
Loyalty Traveler curated Airfare Deals and Google Flights and Kayak Explore tutorials.