Joseph Gordon-Levitt stole our hearts in 10 Things I Hate About You back in 1999, but before that, he played a teenage alien on the NBC comedy 3rd Rock From the Sun. He starred on the show from 1996 to 2001 and got to wear some pretty awesome hats along the way. How much do you love his long hair parted down the middle like that? Now, of course, he's still one of our biggest celebrity crushes and showed off his sexy side as a New Jersey Casanova in Don Jon. Once a cutie, always a cutie.