Of course we all can not forget www.jetweb.se. Good for youth under 26, and student up to 33years. Although it is a swedish site, there are very good deals not involving sweden (example: CPH-ORD). Very good deals can be found by combining two one-way tickets since there is no penalty for one way tickets with jetweb, and by reversing the city pair you can find excellent deals. I rate this site 10 stars.