My wife and I plan to spend three weeks in Europe in May 2012. When is the best time for us to start looking at airfares and where are the best entry cities for airfares?
Zurich has shown some good sales in recent years. I flew there last March for under $600 RT, all inclusive, from SFO, a fare I found in late December, about 2.5 months out. From Zurich, you're not far from Germany or from Italy. London and Dublin often have low rates; Dublin can be a good option even if you aren't really visiting Ireland - Ryanair flies right out of DUB to the continent very cheaply. I'd start looking in January for May. They aren't going to lower fares until they start worrying about filling planes, and it's still too early for that now.
For the heck of it sign up for price alerts via Kayak and special promotions on airline websites. I prefer to fly LAX to LHR (london Heathrow) on Virgin Atlantic if I can. Thus I'm signed up with Virgin Atlantic for price alerts and sales. Two weeks ago they announced round trip tickets for that route would be on sale through Oct 7th at 667.00 plus taxes (total 865.00). Tickets are good through January of 2012. Not a bad deal!
BTW May is a great month to visit. Enjoy.