Picard and Crusher. In "Attached", it seemed the writers had finally decided to get them together, especially since there were only about 10 episodes left, but they copped out.
Voyager kind of messed up it's ships, IMO, as I would've liked Janeway/Chakotay and Seven/Doc. Or really even Seven/Kim would've been preferable. BTW, anyone who likes JC or 7K should read the alternate universe story "Places of Exile" (Hell, even if you don't like those pairings. That story rocks.).
In Enterprise, there was sometimes hints of attraction between Malcolm and Hoshi. For example in "Marauders", Hoshi teaches the Innocent Civilians to fire phasers, and Malcolm stands in the background with a "I think I'm in love..." look.