Also, little pet peeve of mine... why do people in books get married to the folks they fall for at 16? If I married my girlfriend from that time I'd be MISERABLE now. I understand it would be too weird to bring in new characters, but dammit, these kids never even learn basic life skills in Hogwarts and now they're getting married? Yeah, that's safe.
Luna marries Newt Scamander's son (the one who wrote Magical Beasts and Where to Find Them), who wasn't in the book. :P Draco ends up with someone who was in Hogwarts at the time, but never mentioned (Astoria Greengrass). Most of the future stories haven't actually been commented on/published by JK Rowling--they'll come out whenever she publishes her encyclopedia.
The ones who do marry characters from the books:
George marries Angelina Johnson
Neville marries Hannah
Harry marries Ginny
Hermione marries Ron
I'm pretty sure that's all that has actually been revealed.
Of those, only Harry/Ginny and Ron/Hermione dated while in school. Neville KNEW Hannah, but there wasn't any relationship. And Angelina was kinda involved with Fred, not George.
As for Arthur/Molly Weasley and James/Lily Potter, it's also not surprising. They make a point to note in the books that, during Voldemort's reign, people were quick to marry and start families, for fear that they didn't have time to do otherwise. If you are looking to be settled by 20, your high school sweetheart is often your only option, since there isn't really Wizard college, and the Wizarding world is a really drawn out place. You literally know EVERYONE around your age in the whole country, because of Hogwarts.
I am SUCH A NERD. D: