As I started thinking of a summer 2014 European getaway, i have been putting Google Flights to work to search for best airfares for the month of August.
On my last trip (late August 2012- early September 2012) I flew round-trip from Newark to Berlin for $650.
Cheapest gateway I can find at this time (mid-November 2013) from Newark is Dusseldorf for $1002 Non-Stop Round Trip on Lufthansa , for example leaving on Tuesday, August 5 and returning August 19, flight leaving at 4:25 pm and arriving in Dusseldorf next morning at 6:10 am (8 hours flight).
When you do a search on same dates with Cologne (33 miles from Dusseldorf) as your destination, best fare is $1557 on Delta-Air France.
For someone like me who plans to spend most of their summer trip in France, budget newcomer Hop! (Air France subsidiary) offers entry fares around $75 one way. Note that these entry fares allow you only 1 carry on bag and you need to pay 15 Euros per checked in bag-luggage if you register your luggage online.
Those going to Brittany from Dusseldorf can fly non-stop to Nantes (morning flights) on Hop! for $75 one way.
For a number of European capitals (Paris, London, Amsterdam), Icelandair offers August fares RT with one stop in Reykjavík for around $1050. Note that return flights to U.S on Icelandair involve an overnight stay in Reykjavík so you have to add cost of hotel room to your travel costs.
(* Illustration from Dusseldorf Tourist Office Facebook page )