Robb Stark - Wynafryd Manderly. The eldest daughter, discreeter, and more level headed than her sister. If Robb + Wynafryd, Wylla would become heir instead, or, White Harbor and Winterfell would "merge". It's a good northern match, the Manderlys being rather rich.
Robb Stark - Margaery Tyrell. Margaery is a perfect southron lady, and shows adaptability, quick wit, and has a good head on her shoulder. She's received the proper education to run a keep and can navigate troubled waters with ease. She did well in KL, and would have done well in the north, too.
Jon Snow - Meera Reed. Howland Reed might accept the match without finding insult in it, and Meera is heir of Greywater Watch. Jon would take her name.
Jon Snow - Wylla Manderly. She's a second daughter, she might be allowed to marry more "freely" than her sister. Jon is the Ned's only bastard son, he grew up in Winterfell, it's clear Ned Stark holds him in high regard - not a great match for a lord's daughter, but not terrible either. A keep would be given them to make the deal more attractive to Manderly.
Jon Snow - a younger Mormont (Jorelle?). Because the Mormonts seems all around cool and laid back regarding marriages. We never hear of a Lord Mormont, Dacey was "an old maid". Maege's daughters were fathered by a bear. The father of Alysanne's children is equally a mystery.
=> on the why of these matches for Robb and Jon: Jon despises southerners and looks down on them, that much transpires from his POV at the wall. He admires independent, strong headed women (Ygritte, Alys, Val, Arya). He's also a "bastard," so he can't expect to make a great match - while at the same time, he's Ned's bastard, and well loved by his father, so it's not unfeasible that he could have married "above" his station.
Robb doesn't seem to have the same prejudice against southerners, and (that's how I see him anyway), has a more classical view of gender roles, due not only to his mother's influence but also, Theon Greyjoy's. You can't get more "classical" than Jeyne Westerling, a pretty, sweet, shy and naive girl.
Sansa Stark - Domeric Bolton, in a hypothetical scenario where many didn't die. According to his aunt, Domeric was gentle, not at all like his father. He was also a knight, and loved to play the harp. A Stark/Bolton match might have eased the enmity between both houses.
Sansa Stark - Harold Hardying. Harry the Heir is actually a pretty good match. He's handsome, boyish, a knight. The old Sansa Stark might have loved him. Politically speaking, he's heir of the Vale...at the same time though, Robert Arryn stands in his way. From Ned's POV, Harry/Sansa would not be the best match.
Sansa Stark (or Arya) - Edric Dayne. House Dayne is a minor, yet strangely important, house. Edric seems like a nice, serious boy, he's lord of Starfall. Whoever marries him would become the lady of the Keep. That role would probably fit Sansa better. Still, the match would be a good match for Arya as well. Any place that allows Arya some freedom would be good.
Arya Stark - Trystane Martell. As a second son and third in line for his father's seat, Trystane, like Oberyn Martell, is quite free to do as he pleases. Arya would have flourished in dorne. Together, they could have traveled anywhere they wanted. It's a good match, since Dorne has been isolated for too long after Robert's Rebellion.
Arya Stark - Mormont sisterhood
Bran Stark - Lyanna Mormont. With a castle of their own.
Rickon Stark - the daughter of a Flint, a Norrey, a Liddle, or a Skagosi.