Originally Posted by
Sutekh
Definitely Rachel and Ilyanna. Both have been friends with Kitty, and then kind of abandoned by her as she went off to do her own thing. Both have super-tragic backstories involving other worlds / times, and a smattering of time-travel / time-manipulation, making them ideally suited for some pretty far out adventures together.
Gambit and Longshot, mentioned above by darkgreed, would also be an interesting team up. Longshot's naïve innocence, matched with Gambit's bad-buy worldliness, could be a fun mix, since they are so similar (with their acrobatic fighting styles) in one respect, and so utterly different in personality. Either of the two and Nightcrawler, or even Nightcrawler and Shatterstar, could be a similar match-up, all super-agile and fluid and swashbuckling swordsmanship, and yet very different and distinct characterizations.
Sage and Forge might also be a neat pairing (or even a romantic couple!), or Bishop and Cable, or various others who seem quite similar, thematically, but are quite different under the hood, such as the 'force field ladies' (Unuscione, Cecelia Reyes, Skids, Armor/Hisako).
Totally crossing streams and having Scott and Lorna on a team, or Alex and Emma on a team, could be funky, just to have the 'couples' outside of their comfort zones. Scott and Lorna on a team together (with no romantic hints needed whatsoever!), in particular, seems like a recipe for drama, since Alex seems to have trouble letting Lorna go (or trusting her to stand on her own), as well as an entire spinner rack of issues regarding his brother...
Storm and Colossus strike me as having some interesting similarities, both coming to the X-Men with a sort of innocence and purity of spirit that has been tested and challenged, shaping them into something quite different. While I'm not sure I see them as a couple, they'd make an interesting pair for an extended crimefighting duo/team-up. Ororo would very much 'wear the pants' in that family, but Piotr also has a core of iron under all the gentle artist trappings, and can un-ironically say something like, "I am made of rage!" while snapping a fool's neck.