Booking flights to Europe is an annual occurrence for us and i have to say, no, I've yet to find a go-to site for the best deals. i end up triangulating between expedia, kayak, orbitz, and the airline sites themselves.

Once you're in Europe, if you plan to fly between European countries, there are lots of budget airlines you should absolutely check out e.g. Ryanair, Wizz, BerlinAir etc.

I use a website called Skyscanner i find quite good deals on that.You should check it out.

I second Ryan1. I used Skyscanner to find prices on several flights all at the same time. Similar idea to Kayak, but it takes you directly to the airline's site, allows you to do a flexible search to find the least expensive flight days without doing a pop out comparison between sites.