--A well-written Quantum Leap/Buffy the Vampire Slayer crossover. I can think of several ways to do this, but I've never seen this crossover written, and I think there is a lot of comic (and dramatic) potential to be mined here. (Personally, I'd Leap him into Buffy, but that's not a requirement.)
--I tried writing this one, actually, but other ideas have crowded it out. When Carter is injured during the season 10 episode "A Line in the Sand," we see a different side of her--one who realizes that she might be about to die, and tells her teammate where her personal letters are kept; one who wonders aloud about whether there might really be a God somewhere beyond death to welcome her. I'd love to read a short, 1st- or very tight 3rd-person fic, from Carter's POV, exploring what's going on her mind and heart during this time. (preferably gen.)
--Along similar lines, I'd love to see an author tackle 1st-person Larry Fleinhardt, upon his return to Earth. Especially if the fic at least touches on why he doesn't ask after his girlfriend Megan.
My idea, based on a title offered by whitemartyr:
The Wayward Seven
Jack, Sam, Daniel, Tealc, Jonas, Cam, Vala.
These are the people who have made up SG-1.
So, naturally, these are the people rounded up from various places in the galaxy at the request of a rebellious Ancient to mount a last-ditch secret mission against the Ori.
Will they obey orders? Probably not. Will they manage to get along? Not at first, that's for sure. Will they survive? Who knows?
Can they save the galaxy?
And here is the actual fic: They Won't Fade Away, by dvswraatins