Lux and Ezreal I can see, hugely due to a fan art manga submission where lux was interested in Ezreal but he was lost in his studies for his next adventure to even notice.
Reluctantly Garen and Kat, just because they have history of rivalry.
Ahri is not couple material, she has way too many personal problems dealing with "Guilt" which is still new to her since she was born/raised a fox. And she seduces like, everyone, not the most loyal. (If anything, I'd love to see the conversation Ahri would have with Lee Sin about her guilt. Good Will Hunting, LoL style I'd guess.)
Gangplank and Miss Fortune, for obvious reasons.
... Man, so many non-compatable couples in my opinion. I'm not familiar with Twisted Fate's story but he seems like the kind of guy to attract SOMEONE for a long time. Graves is too grizzled and out for revenge, Riven is kinda a blank slate but has no ties to anyone, Anivia is more of the wise elder sort, Shen has way too much to worry about with Zed running around defiling the name of his order, I dunno. Gotta read up on a lot of stuff if I wanted to make an educated opinion.