Is there anything more relaxing, majestic and undeniably wonderful than air travel? Don't feel as if you need to answer that; it's best not to yell obscenities at your computer screen while you're at work.
Kayak lets you quickly and easily search multiple airlines for the best price on plane tickets. You can track your flight status and book hotels and rental cars too.
It's especially helpful while you're in an airport and you need to book a flight to replace the one you just got bumped from for no good reason. Maybe yelling all those obscenities had something to do with it.
See also: FlightTrack Pro, TripAdvisor, Hotels.com, Priceline