Well, its obvious K/R would win. Since it is the ONLY relationship in the series that is not only implied and in detail but actually confirmed. D/S is just subtle hints (other than emotion sickness but that doesnt count).
Bonnie & Brick, maybe, sometime later in their lives. Even though I found Brick to display maybe a bit of interest in Kim in Season 1 (esp. in All the News). I mean what else could it mean when he told Kim what she was doing was C-O-O-L (that's cool right?).
Ron/Shego - maybe at one point Ron might have had a school boy crush (eg. Tick Tick Tick) but its not mutual.
Drakken/Kim - After that punch at BN HQ, I'm inclined to think not
Felix/Monique - I dunno about this one. As mentioned above, they never met, at least not on-screen.
Kim/Shego - see Drakken/Kim. "You know what I really hate?" "That your date melted?" "Nah, You."
Drakken/Ron - Who comes up with these things?
Ron/Tara - He DID have a chance... (maybe) until he blew it with his bad boy act. "That's just eww, Ron"
Tara/Josh - Well, lots of gray areas here. Tara, for instance was seen holding hands with Josh in Emotion Sickness, but was seen dancing with a mystery guy at the Junior Prom.
Kim/Josh - "We drifted apart" nuff' said.
Yori/Ron - Plausible, but she's living halfway around the world. Kim is the Girl next door.
Zita/Ron - Hard to say, since they never shown what happened after Vir-Tu-Ron. But I would really have liked to see Ron hang out with Zita again (and blow the other half of his chance with her away).
Kim/Eric - Only if he's real, which he is not.
You know, sorry for deviating but I really enjoy writing these ;D
Oh, yes, and I picked K/R. Seriously, I don't really have any other choice, do I?
EDIT: oh, you forgot Ronnie & Bonnie
But other than the fact that their names can rhyme, they have little in common. Though I have a feeling that only Ron can tolerate Bonnie's behaviour here. Tough luck Bon-Bon.