- RLM Systems/FlightView.com lets you search for flights by airline and flight number or by city and time. Be sure to check out the airport traffic map which shows flights going into and out of major U.S. cities.
- FlyteCom/WebTrax provides flight tracking, and also provides information about all flights between an arrival and departure airport you specify.
- Flight Explorer FastTrack offers a number of different ways to track flights in addition to airline and flight number.
- Fboweb.com offers many services for flying geeks, including a "airspace navigator" toolbar. Most services require a free subscription to access.
The first one is fun if you just keep clicking on the "Let us find random flight for you!" and-help-you-waste-more-time-at-work-button.