The price is going to vary depending on when and who you travel with.
For the Scheduled airlines (BA, Virgin, American etc) the season tend to work...
Low Season (Cheapest) Jan to March, November till around 10th Dec ish
Shoulder/Mid Season April (exc easter) - 30 Jun, Sept & Oct
High Season (Dearest) Jul & August & 10th Dec ish - Christmas
The fares sometimes drops down slighly around the 23rd August in comparison with the rest of August. Christmas peak fares usually start applying around the 10th but can drop from xmas day onwards. Easter varys but is usually not as high in price as Summer/Christmas.
Weekends (Fri, Sat Sun) are usually £20 per person more the Weekdays
Bear in mind that school holidays dates sell out fast and will put the price up.
Sorry can't help so much with the charter flights (TUI, First Choice) but they usually have big increases during the holidays.
This year we had to pay about £650 pp to travel in August with flight via Chicago, the direct flight were around the £850 mark

. In May 08 we pay around £600 for direct Virgin flights.
Happy planning
