@Porche:
I think aside from the obvious HancockxLuffy (which is clearly stated as one sided) the only logical pairing is Luffy and Nami.
Just as logical as Luffy/Robin.
And heck, Luffy/Vivi, since Mayumi Tanaka is supportive of that pairing.
(even though I prefer Vivi/Kohza)
@Porche:
As for there not being "subtle" stuff, Nami is the only one who is allowed to wear Luffy's hat. He places it on her himself early on in the series (Arlong). While it was to comfort her, you notice he doesn't offer such a privilege to Chopper, Zoro, or anyone else in need of reassurance. (Please correct me if I'm wrong here.)
I don't need to respond to this because Sai-chan already did so.
@Porche:
I really don't think someone like Luffy's character is designed for anything more than friendship but, should any canon pairing pop up, the most likely would be LuffyxNami - according to their close friendship and his respect for her.
He doesn't have any more or less respect and friendship with her as he does with anybody else. If anybody is closest to Luffy, it's Zoro and not Nami.
If anything, Nami is closest to Usopp, because they're stuck together very often and can relate to each other the best -which was actually brought up several times. Not to mention that Usopp is canonically attracted to Nami (while with Luffy and Chopper, Oda dismissed it as being a copycat and pretty much confirmed Luffy is completely asexual).
I still think Usopp/Kaya is preferable and more likely, but Usopp/Nami has a lot more going for it than Nami/Luffy.