This site provides flight information to help you plan a trip. You can calculate things like the straight line flight distance between cities. Or if you're taking an international flight and you want to plan your arrival time, check the flight time between airports. You can also book a hotel near the airport.
If you're planning to travel overseas to another country, you might want to search for the closest airport to your destination. Or you can browse all of the major airports in any state or country. To compare flights, check the list of airlines that fly to each airport.
Finally, if you're interested in finding out more about carbon offsets for your flight, make sure you figure out the carbon emissions for your flight.