My post below, inspired by a happenstance viewing of Michael Curtiz's great 1939 Dodge City, inspired some astute commentary both on and off its thread. Some readers were moved to cite their own favorite dissolves. A particularly persuasive citation, drawn from Orson Welles' 1941 Citizen Kane, by commenter Charles Hartney:"The scene in question occurs during Kane's first encounter with Susan Alexander, when she provides him hot water and he the necessary comic relief to alleviate her toothache. He starts to question her about her age, her occupation, what she wanted to be when she was little - "A singer," she responds sheepishly - and then asks that she sing for him in the parlor.
Susan begins to sing as Kane regards her approvingly, though her voice is tinny and her piano-playing unintentionally dissonant. It is here where Welles inserts a dissolve, and the resulting scene is very familiar: Susan at the piano, singing the same song, and Kane rapt with attention. But the scenery is changed: we are no longer in Susan's claustrophobic parlor, but in a more refined, capacious environment. Susan has changed as well: her dress is more elegant, her piano playing and singing smoother, more melodic, confident.
These elements suggest a number of narrative developments: a significant passage of time; that Susan has been given the freedom (see: money) to pursue her childhood dream of becoming a singer; and not only the continuation but the deepening of the relationship between Susan and Charles - he has obviously moved her into more luxurious surroundings.
Watching Kane for the I-don't-know-how-many-th time, it struck me what a formal marvel this transition was. To communicate so much with so little...astonishing."
Here are screen captures of the, let's say two-and-a-half shots in question:
Indeed, a whole dissertation could be written on the change of interior lighting apparatuses alone...
In an e-mail, my friend Joseph Failla notes quite a few things: "One of my favorite dissolves (can you believe I have favorite dissolves?) is in SEVEN CHANCES  when Keaton gets behind the wheel of his auto and instead of driving off, the background dissolves to the location of his destination without any movement at all. It's a weird moment that at first feels very disorienting but actually makes plenty of sense in an absurd kind of way..."
"I also remember some very striking use of dissolves in SHANE , in particular a sequence with Jack Palance crossing a barroom as he fades from the background into the foreground. It's a great touch which gives him and the sequence a suitable sense of menace..."
What's super-interesting about the dissolve in Shane is that director George Stevens is more often cited as a great cinematic storyteller rather than a visual stylist. But there's literally zero diegetic function served by that dissolve; not only that, but there's no rational reason for it to exist at all. It's absolutely right, of course, but it's right as a stylistic flourish, something of the sort that Stevens doesn't have much of a reputation for. It's because of this bit that I tend to look at all of Stevens' work harder than I might have. I believe that Scorsese, also, values Stevens as a stylist; whenever I've heard him refer to, say, the content-problematic Giant, he always specifies that for him its greatness is "visual." I also find that much of Shane is rather explicitly Eisensteinean, but that's something for another time, another post.
Back to Mr. Failla: "Of course there's the crucial sequence in THE WRONG MAN  when we get that long slow dissolve from an at the end of his rope Henry Fonda, praying for a miracle in close up, to the hold up man Fonda has been mistaken for, as the scene switches to his point of view."
Indeed, and this is worth going into at some length...first in terms of screen caps, because it's a long dissolve. I'm also including the shot prior to the dissolve, of the picture of Christ that Fonda's character prays to.
There's quite a bit that's extraordinary here; first off, the rather staggering notion that Hitchcock is taking the idea of an answered prayer at 100 percent face value and absolutely unironically depicting one. And that's not the only reason that the word "Bressonian" springs to mind when considering this sequence; there's the lean, impassive face of actor Richard Robbins as the actual right man, that is, the guilty party of whose crimes Fonda's character has been unjustly accused. It's a very Bressonian face, at the same time as being rather absolutely American. I also like how Fonda's and Robbin's right eyes (left side of the frame) line up pretty much exactly at one point during the dissolved; boy, is that a purposefully locked-down camera(s), or what? In Hitchcock/Truffaut, the auteur under examination requests that Man be filed among "the indifferent Hitchcocks," and Truffaut protests, "I hoped you might defend the picture." It's easy to understand why. The quasi-documentary feel combined with a high level of very intelligent stylization, the psychological acuity and the unstinting perspective on the story's valleys of emotional bleakness—all these became signal features of Truffaut's The 400 Blows, and quite a few other movies of the French New Wave.