7. Katee Sackhoff
Howard's fantasy girl has made two cameos in The Big Bang Theory, showing up in seasons three and four. Her first cameo was in the 'The Vengeance Formulation,' appearing in the bath as she questioned him over Bernadette, leading his proposal later in the episode. This also results in possibly the show's funniest moment as he sings a song in The Cheesecake Factory. Sackhoff's second cameo came in 'The Hot Troll Deviation,' appearing with George Takei as she questions Howard about his latent homosexual tendencies and offering advice as he gets back together with Bernadette. This cameo gives us a great insight into what goes on in Howard's mind, and also teaches us a valuable lesson never, ever go in the bath after him.