4. Colossus
Colossus is easily one of the X-Men's best and most formidable characters, yet he's had a pretty short shrift as far as his cinematic portrayals go, being relegated to a brief cameo in X2, and then a forgettable appearance in The Last Stand. However, Days of Future Past certainly gives him a real opportunity to shine, as he figures into the plot to a fair degree, and the exploration of his relationship with Kitty Pryde should make for compelling viewing if they decide to include it. Above all else, I just want to see a guy ricocheting bullets off of his stunning alloy frame, and there definitely hasn't been enough of that in these films so far. What would be more of a challenge is actually conveying the emotional state of his character rather than just making him a glorified metal shield, but if there's anyone up to the task, it's Bryan Singer.