5. Dead Denny Duquette returns to "Grey's Anatomy," ABC. Denny (Jeffrey Dean Morgan) died of a bad heart back in 2006, but he returned this fall, at least in the hallucinations (or fantasies?) of the love of his life, Dr. Izzie Stevens (Katherine Heigl). Not only did Izzie converse with Denny in front of her colleagues (who can't see him), but she had passionate, loud sex with him (leading her roommates to conclude she was, uh, you know . . . being with herself). Though the show reportedly plans to explain why this is happening, viewers can't be blamed for suspecting it's just a lame way to revive a popular guest star or give a disgruntled cast member an interesting plotline.