I agree, if they make more movies, it needs to be Heir to the Empire. Those books captured the sprit of the old movies and would bring back the original characters in a better way.
You don't need to order the books online, just go to Borders and look in the science fiction section for the books Dark Force Rising(book 2 on the heir trilogy, and The Last Command(book three).
Luke asks Mara to marry him in the Thrawn Duology books 2 Vision of he Future. They don't get married in the books rather a comic book covers that, but your not missing anything, its rather short. If you want a good book on their relationship after marriage go for Survivors Quest, which takes place a year after they are married.