I like to use the search engine at Orbitz – let it check a few days before and a few days after you plan to go, too. There are bargains to be had by flying on certain days.
Tuesday afternoon is the best time of the week to purchase a ticket.
Where are you going? I may have some tips on bargain airlines for you.
Last winter, we flew to Florida twice, once paying $29 ea way, and once paying $49 ea way, plus $30 to check our bags.