It's a good time to be digging for cheap flights. They're everywhere. There's a Southwest fare sale happening through March 29, cheap round-trip tickets to London, and absurdly low prices on flights to Hawaii.
Add this sale from WOW Air to the list. The sale has cheap flights out of 13 US cities to locations all over Europe, including London, Berlin, Paris, Brussels, Copenhagen, Stockholm, Barcelona, and many other worthwhile destinations.
However, the cheapest tickets are to Reykjavik, Iceland. You can find one-way flights for $99.99 (and in many cases round-trip fares for $199.98) out of Boston, Chicago, New York, Pittsburgh, and Washington D.C. There are also enviable prices to Reykjavik flying out of Cincinnati ($104.99), Cleveland ($104.99), Dallas ($149.99), Detroit ($119.99), Los Angeles ($129.99), Miami ($279.99), San Francisco ($135.99), and St. Louis ($104.99).