George Takei, a.k.a., Mr. Sulu of Star Trek fame, makes a guest apperance in episodes 13 and 14 of Heroes. I just had to take this screenshot of the closing scenes of episode 14. Note the license plate on the car.
That said, I felt the appearance was wasted. Takei plays Hiro's father, but it left me wondering how it advanced the Hiro and Ando storyline. Was it simply done to play to the Trekkie fanbase that intersects with "Heroes?"
If they actually do something with it in future plotlines, I will have been proven wrong. But so far, it only manages to introduce one additional facet of Hiro, and not a very interesting one at that.