Frink -

Yes, Buffy and Angel are both Joss Whedon shows. He also wrote the script for the movie, but it got changed somewhat significantly between him selling it and the movie being made. The first season of the TV show is a sequel to his original script for the film as opposed to the film itself.

And I do highly recommend Firefly. Don't forget about Serenity, the Firefly movie - it takes place after the end of the series. (Though my roommate, who loved the show, didn't like the movie for some reason.)