Airfare Watch

The wife and I are going to London in late March. I checked British Airways every day for two weeks, and finally got in on a sale they were having. I paid $644 round trip for each of two seats, and then upgraded from coach ("World Traveler") to Coach Plus for $139.
We thought we got a great deal when we went to London in September at a cost of $724 each, (plus $129 upgrade) but for our upcoming trip in March it was even better.
So keep checking the various airlines' websites, and when you find a good price, take it.

Being that September is still part of the high tourist season, $800 would be an excellent fare for that time of year. Several websites already mentioned (and others) offer fare alerts for various city pairings. From Maine, another potential location for cheap fares would be from Burlington, VT....some times, you can get cheaper flights out of smaller airports, rather than the connecting city that you may go through. However, Montreal, and certainly Toronto, are too far for you. If you have a connecting flight, you may want to explore Halifax as a possible airport of origin.....but Boston will probably be your best bet.
As well, sign up with any airline that flies from your area to Britain. Their specials can be very limited in term of time, and e-mail alerts are a good way to follow them.
Keep your mind open to alternative destinations in Britain. You may find cheaper flights into cities like Manchester, Glasgow, or Edinburgh than you will to London.
Set a price you're willing to pay, and when you find something close, buy it and move on with your planning. Don't assume there will be seat sales one, two, or three months before your departure. With airlines monitoring their capacity on an almost minute-by minute basis, the best deals can come at any time. In the past two years, the best price for my flights to Europe have come 9, 8, 8, and 6 months before departure dates, respectively.

Does anyone have a good way to organize the info when tracking fares for comparison? My husband and I are using a shared Google spreadsheet to record fares daily--a bit compulsive but it's helpful. We're looking at fares for May/June travel.

Not sure if anyone mentioned setting up daily e-mail alerts on Kayak.com...

Thanks Everyone! I'm not against flying into places other than LHR, just figured that would always be the cheaper...No confirmed itinerary or even specific flight days yet, as we're waiting for time off confirmation from work for both my husband and I. That won't be until the end of January. We hope to visit the Cotswolds, Edinburgh, and daytrips from Edinburgh, and if time allows, York & London. Hopefully a 10-14 day trip, travel by train, with likely an exception in the Cotswolds. That said, what are your thoughts and suggestions about flying open jaw? Thanks again.

Open-jaw? For sure. It'll cost you and your husband at least $150 to get, say, from London back to Edinburgh, plus a day of your vacation. Check both types of flights, but, to paraphrase Clint Eastwood, you gotta ask yourself one question...how valuable is that extra day to you?

Since you are talking about spending time in Edinburgh, look at flying into Glasgow also. When I had to make a last minute flight to Edinburgh, it was about $500 cheaper to fly to Glasgow even with an open jaw returning from London. It is an very easy train ride into to Edinburgh. Just a thought.