Looking for the cheapest flights from Boston to Great Britain.?

I've searched a lot on Travelocity and Priceline, and by tweaking departure and arrival dates, I have found prices a little less than $1100 per ticket. We're planning on leaving July 17th or 18th (can't be flexible about that), and want to stay for about 10 to 15 days. We won't be needing hotels since I have some family and friends currently residing there. Acceptable airports for arrival are London-Heathrow, Glasgow, Edinburgh, Birmingham, and Belfast. Do you have any particular recommendations to find better prices? I don't fly much so I don't have much experience hunting for airfare bargains. Would it be better to wait, or will prices just climb between now and then? Thanks!