5. Cyclops | 6. Jean Grey
I love James Marsden and I love Cyclops. I hate how Marsden's Cyke was portrayed in the "X-Men" films, especially the way he was sent off. "Days of Future Past" presents an opportunity to retcon a sh---y ending for one of the most iconic Children of the Atom; give Marsden the material his talent deserves, and I promise you, fans will get the Cyclops they've always wanted to see. Story-wise, there's the Havoc-connection already in place, so there are certainly reasons to have the X-Men field leader back in the mix.
Bonus: Jean Grey. She's dead and that's fine but Famke Janssen is awesome and that's enough to warrant at least a cameo, says I! (And it seems like others agree.)