Something I've always been intrigued to try but absolutely never found a partner to bite for is a Starcraft II roleplay, involving perpetual ne'er-do-well turned roguish Lawman, and ultimately resistance leader Jim Raynor, across from the woman of his dreams and nightmares, ultimate badass psionic assassin turned nigh omnipresent swarm-queen slash immortal force of nature, Sarah Kerrigan.
The two have some great chemistry that unfortunately just... never quite gets to manifest in the series. The love is there, the mutual admiration and respect, and even after both of their worlds have gone to hell in a handbasket, dragging them to a place where neither one can abandon their personal wars to be with the other for fear that the galaxy would tear itself asunder for their absence, but it never seems to solidify. I've always wanted to explore that a bit with someone who loved the story the way I do.
That and I'd be very interested to see what kinds of creative ideas that the kind of person who'd endeavor to play the Queen of Blades would come up with. Not quite your typical role, which I always felt makes it all the more interesting.