Building a SciFi/Fantasy Library discussion

I've fallen hard for Leto II and Ghani in Frank Herbert's Dune and I would like to read more sci-fi/fantasy books that portray a very, VERY close relationship between two siblings. I don't care if it's an outright - but consensual! - incest or soulbonding or merely "them against the world" kind of things. Just something that made you as a reader go all "Wow, they are close!"

Examples: Leto II and Ghani Atreides (Dune), Sam and Dean Winchesters (Supernatural), Ukiah Oregon and Atticus Steele (Dog Warrior)...

Well, I've been watching "Game of Thrones" on HBO, and though I haven't read the books yet, there is a very close relationship between two of the major players in the 'game': The Queen and her brother.