Starfire kisses Robin to learn English, in the episode GO! They kiss in Trouble In Tokyo, at the end, and finally become an official couple. In the GO! version, they don't kiss, though in the episode 'Dreams', Robin dreams of it. In the episode 'Puppets, Whaaat?' Robin makes the puppet of himself and Starfire kiss three times.
Yes, in "Go!"(Episode 62) they do but that's only because Starfire needs to learn English. But in Teen Titans: Trouble in Tokyo (the movie) they kiss after the battle with Brushogun's main ink monster.