Free flight tracker that shows registrations?

I don't think so. That's important to the airline, but not to ATC. ATC normally tracks aircraft by their callsigns, not their registrations. For private aircraft, they're usually the same. For commercial aircraft, the airline's callsign name and flight number is normally used.

I concur with the previous answer. Flight trackers are based on data from the ATC system. When flights use callsigns and flight numbers, their tail number is not associated with it anywhere in the ATC system, thus not available for tracking.

if you find a tracker like that which works, myspace will delete your profile - they are not allowed on myspace