By couples, they mean people who are in a relationship, so no bromances or good friends with never-resolved sexual tension in this list, sorry. The couples are not listed in any particular order. The list might contain spoilers if you haven't read the books.
#1 Ron and Hermione from the Harry Potter series. I don't care that J.K. Rowling thinks that she should have ended up with Harry, they still make a cute couple.
#2 Jaime and Cersei from the A Song of Ice and Fire series. They are ment to be and you know it, don't try to deny it.
#3 Lola and Cricket from Lola and the Boy Next Door. They're perfect for each other.
#4 Inspector Mascarell and Quimeta from the Inspector Mascarell series. It's the kind of life-long love that you expect to find. I'm especially fond of her, especially as she still appears to him through his thoughts even after all the years she has been dead and even though Mascarell has found himself a younger wife.
#5 Robert Jordan and María from For Whom the Bell Tolls. Few times has love been described so precisely as in this book. Why haven't you read it yet?
#6 Gen and Carmen from Bel Canto. Love appears in the most unexpected places and situations.
#7 Bridget and Mark from Britget Jones's Diary. Surprised? You shouldn't be.
#8 David Copperfield and Agnes from David Copperfield. It took David an eternity to figure out what the reader figures out when Agnes is first introduced, but at least he figured it out.
#9 Wesley and Buttercup from The Princess Bride. As you wish.
#10 Viola and Orsino from Twelfth Night. You might think it's a weird choice because he had the hots for Olivia before Viola appeared disguised as Cesario, I think that, deep inside, he kind of develops feelings for her male version and is relieved to find out that she's a woman. Or I'm reading too much into it, who knows.