For the obligatory Disney example, Simba and Nala. They both bring out each other's strong points and help them with their downfalls. Nala encourages Simba to be humble and responsible; he encourages her to be brave and dedicated. They were kids together and remained (emotionally) loyal for many years of separation, and still loved each other even though both of them had undergone vast transformations. I'd say out of all the Disney couples, theirs is both the most compelling and the best example to set for kids.
Out of classic literature, I'd have to lean towards Winston and Julia from 1984, if only because most older novels focus on horribly unhealthy (Wuthering Heights) or incredibly sexist (everything Greek). Theirs is a romance as much intellectual as physical or emotional, and I really like it for that. Yes, 1984 is depressing and their romance, predictably, ends on a depressing note, it is worth considering that their shared discovery of the forbidden fruits in their grimdark Garden of Eden was the high point of the book. What they share is the greatest example of self-expression, and they are allowed to be themselves around each other and only each other. I can safely say that, of the books I was assigned to read in high school, 1984 was the only one which had a love story that interested me.
In contemporary film, I'd probably go for Tony Stark & Pepper Potts from the Marvel Cinematic Universe. While in the first Iron Man they were cute, the development between them and of Pepper's character is fairly superb. It helps that the actors have good on-screen chemistry, but the writing is what really brings them out as a couple. They complete each other in no small way, help each other through hard times and celebrate the good- and they are equal partners in the relationship, which is something that a lot of film couples can't say. One is usually clearly in charge, with xir partner being along for the ride (read: every action hero's girlfriend is useless). In an almost-unique example, especially for superhero movies, Pepper is allowed to take charge formally, not just behind the scenes, and is shown to be incredibly intelligent, organized, and arguably a much better leader and follower both than her SO.