Here will be our attempt to get them all in one place and, if we miss it, to give readers a chance to comment below and add to the conversation.Characters like Ink, Spyke, Toad and Havok (the four mutants Mystique comes to rescue in Vietnam) might have felt like cameos, but we'll exclude from consideration mostly because they actually had an action set piece and got to use their powers; that's as much time as we got from a number of the ostensibly-major characters, and so they can stand on their own.
Claremont, who wrote the original "Days of Future Past" story and whose other works have inspired X2: X-Men United, X-Men: The Last Stand and The Wolverine, gets a cameo for the first time since X-Men: The Last Stand. Last time around, he was fairly vocal about not having an on-screen credit for The Wolverine in spite of marketing materials that emphasized the filmmakers' focus on remaining true to the source material he wrote with artist Frank Miller.
Like Claremont, Wein plays one of the U.S. Senators in the film. Wein is credited as the co-creator of Wolverine, as well as two other characters in the film -- Colossus and Storm.
Sigel, a frequent Singer collaborator who has worked on all three of his X-Men movies as well as other projects like Valkyrie, appears briefly as a disguise Mystique assumes to escape Magneto at the Paris peace talks.
Killed in X-Men: The Last Stand, James Marsden had assured fans that there wasn't enough room in a crowded movie like this for Cyclops to be resurrected. Turns out he was wrong about that, and Cyke appears in the film's final moments, one of a number of things "set right" by the film's ending.
Another fatality of the previous installments who was "un-killed" by the events of this film, the time tinkering that Wolverine did in 1973 has apparently restored the love triangle between the X-Men's most popular character and two of the team's founders.
She was also last seen onscreen as a spectral form haunting Wolverine's conscience in The Wolverine, so it's nice to see her there and so happy to hang out with Logan.
Kelsey Grammer's Beast
At one point, Wolverine tells Hank McCoy that in the future, he isn't one of the ones who survives the Sentinels' onslaught -- but following the events of the 1973 attack on the White House and the cancellation of the Sentinel program, we see Cheers and Frasier star Kelsey Grammer, who played Beast in X-Men: The Last Stand, appear in the X-Mansion.
The fact that he seems to be basically the only thing other than Ellen Page's Kitty Pryde held over from The Last Stand is somewhat beside that point.
(Thanks to commenter "X" below for this one.)
After being one of the main characters in Singer's first two X-Men films, Rogue barely appeared in X-Men: Days of Future Past and, as far as anybody can tell, may have been added back in at the last moment.
A subplot involving Rogue that would have seen her play a more key role in the final version of the film was cut completely from the movie for time and because it wasn't propelling the main story forward, leaving her with almost no scenes.
Later, though, a report came that they were doing reshoots, and that more Rogue might be added. If that happened, it isn't really reflected much in the movie...but she does appear briefly, in the final scene and once again romancing Iceman as she did in the early movies (as an added bonus, Kitty Pryde and Colossus, who were together for a long time in the comics, are also together there).
Another commenter below, J-Nel Gozo, notes that it seems to be the film's director Bryan Singer who is shooting all that footage in Paris after Mystique falls out of the building and pandemonium breaks out.
It's easy to imagine that's right, even though we didn't spot it, since one of the stylistic choices made in the film is to follow that cameraman's output intermittently for a few minutes during that sequence, while he tracks Mystique and shows off others. The footage is reused later as some of the first shots of mutants in the world, a parallel to Singer's actual role as the first one to direct these characters in live action.