This will be very incomplete since I'm fortunate enough to have adventured with many skilled players ^^; Kinda going off to the top of my head:
Ashn - RDM: Honestly, he's one of the best RDM out there in my biased opinion. Why? Because you'll *never* have to ask him for a refresh, dispel, or to sleep an add. He's everything you'd want in a support-role, so smooth you don't even notice how well the party mechanics are working with him oiling them.
Caboose, Meyoh and Nif - PLD: I'm lumping these three together because I adore them all for the same reasons. I tend to play DD jobs and I as a DD I try to be mindful of my hate generation. These gents have always guarded me when I've gone too far (it happens, especially when I'm a MNK against bones =/ ) Nif has an uncanny ability for knowing right when I've pushed things to the edge. (I'm impressed when, as a RNG, I can have Warcry + Sharpshoot + Barrage scorpion arrows and the mob only takes a single shadow off me before Nif has the hate under control again.) As a DD, I feel very gratified when I have the freedom to push my output further because I'm not griefing the tank by doing that.
Valamir - BRD: Picture this scenario: BLM AF3. An alliance of 2 parties, no tank except for the MNK (me) and it's been a very long night of mishaps already. We'd done the fight twice already (I died both times) and the third party abandoned us. We were up for one more fight before everyone had their Hats. I did the best I could, but I died again, and from my vantage point of sucking sewer floor, I saw one of the most amazing things. Not only was this hodgepodge 2 party alliance tackling Magic Sludge valiently, Valamir was keeping all of the links at bay. By the time they were done I counted no less than 7 links that he'd expertly kept asleep until the alliance recovered enough to clear them out. This wasn't the last time I've witnessed him manage a horde of mobs that would seem impossible with a lesser BRD (especially if they panicked during the onslaught). Whenever I party with him, I consider myself lucky ^^
Nyiri - RNG & Moriggan - THF: I lumped these two together 'cause they're another pair that have accomplished "o.O; How did you do that?!" type feats. Maybe I'm too easily dazzled, but I don't think so. This time, the scenario is Garuda Prime battle. PLD, MNK, and WHM are dead. Only people still alive are Valamir, Nyiri (RNG/NIN), and Moriggan (THF/NIN). Man, I wish I'd've taken pictures of it. With Val backing them up, Nyiri and Mori out blink-tanked Garuda. It was a nervewrecking battle to be sure 'cause she kept healing herself, but also exhilerating to watch. And just to prove that it wasn't a fluke, Mori and Val finished off Titan Prime using the same method (Nyiri had fallen.) And Nyiri, Mori, and Val did it to Levithan as well. It was just, piles of cool to watch them work together.
Though I haven't played with either of them in forever, Bladegash and Decepticon (both RDM) left an impression on me. Like Ashn, they're very good at what they do :)