Which Show Has the Best First Episode You've Ever Seen?

A great first episode can make you fall in love with a show immediately. Sometimes, the story grabs you from the opening scene, the characters are instantly interesting, or the ending leaves you desperate to watch the next episode. Which TV show has the best first episode you've ever watched? The kind of pilot that had you hooked from the very beginning and made you think, "Yeah, I'm definitely watching this!"