I've just read this on Wikipedia -
"The show has five complete seasons, all of them are available on DVD. The show was renewed for the fifth season on February 27, 2007. On March 2, 2007, it was announced that James Caan and Nikki Cox would be leaving the series. Caan's departure is because he wants to return to acting in feature films, while Cox's departure seems to stem from budget cuts. Tom Selleck replaced James Caan as head boss in season 5. In the final season, only 19 episodes of the originally planned 22 episode season were filmed at the time the show was cancelled. The final episode was a cliffhanger with many issues left unresolved and will remain unresolved according to TV Guide Canada. However, Michael Ausiello of TVGuide said that there are plans, should a proper resolution not be possible, to have the characters of Danny McCoy and Delinda Deline cameo in an episode of Knight Rider carrying a newborn."
So basically, no more! How can they cancel it?! It was sooo good! And how else am I going to get my Danny fix? :o(