FlightAware - Live Flight Tracking
TripIt - TripIt is a travel app that creates a master itinerary to organize all of your plans for your vacation or work trip in one spot.
RadarBox - Real-time flight tracking app with one of the best and most accurate coverage worldwide.
Sygic Travel Maps - Itinerary planner for independent travelers
ADSBExchange - The world’s largest co-op of ADS-B/Mode S/MLAT feeders, and the world’s largest public source of unfiltered flight data. Access to worldwide flight tracking data for hobbyists, researchers, and journalists alike.
Travelchime - Google Docs for planning your trips with friends.