+1
"Firefly" and "Journeyman" have already been mentioned, but I also want to add "Nowhere Man" with Bruce Greenwood, "No Ordinary Family" with Michael Chiklis, and "The Class" which was a Friends-type of ensemble show.
But IMO, the absolute worst cancellation was the show "Stark Raving Mad" with Tony Shaloub and Neil Patrick Harris. This was an "Odd Couple" type of show with Tony Shaloub as a Stephen King type of horror writer, and Neil Patrick Harris as a Monk-type of character.
It only lasted one season, and it won the People's Choice Award for Best New Comedy, so of course NBC cancelled it. Most of the episodes are on YouTube, and I highly recommend it. It was one of the funniest shows on television EVER.