To plan your trip: hipmunk.com.
Best for: Comparing air and train travel.
Winning features: Hipmunk lets you sort flights by cost, duration, departure or arrival time, or level of “agony” (think multiple connections or a super-pricey ticket). When applicable, it also includes Amtrak in the results—a boon for those who like riding the rails.
Weak spots: The site has an offbeat way of displaying results: It presents each flight as a bar stretching from departure to arrival time. Some people may find this difficult to decipher.