WOW! This is really cool
Flight tracking on the www simply does not get any better than flightaware.com. As of 9 Jan, 2006 at 1220P, this free site claims to be currently tracking 4,308 IFR aircraft and 309 VFR aircraft with 14,019,891 total flights in the database. They have tracked 38,847 arrivals in the last 24 hours.
Flightaware.com sifts through the FAA's ATC data and offers it any number of ways. Links are everywhere, so if you want to see only the Cirrus SR22's currently in the air, can do. Want to find out what is inbound to your patch, can do. Want to search by flight number and get a cool history of that flight over a number of days, to see if it stays on schedule or has experienced delays recently? Can do that too.
Here is live flight tracking (from earlier today) for Eugene Mahlon Sweet Field, my home field.
They also present Quicktime animations of flights that have been in the news. Here is a track log animation of N225GV's flight on morning of November 21, 2005. The flight (operated by Nike, Inc.) encountered landing gear problems after takeoff and attracted national media coverage during the six hour local flight before an uneventful landing. This is not a joke.
Lastly, if you just want to track one flight across the country, this site has the most comprehensive tracking system I have ever seen. Like I said...wow!