I have used Orbitz on a number of occasions and have found they offer very competitive fares. The others I use frequently are Travelocity and Expedia - I would recommend you search each to see what your options are.
Thanks to all for the helpful info about Sanford - I will definitely be using it for my family's Feb '05 trip - the departure airport in NH is much closer to home for us than Boston, the parking at NH airport is free, the flight is direct...what more could you ask? We're renting a car once we get to FL, so transportation from the airport isn't an issue.
A bit further away from everything apparently, but I'll trade that for smaller/quieter/simpler airport experience.