I've only done a few single-panel flashbacks in my comic so far - when something happens that triggers a character's memory of what has happened previously, but they can't speak it out loud - but I am gearing up to do a much larger one later on in the story, which I will probably handle as its own separate chapter? Like, start it off with a short scene in the present to prompt the flashback, then go through the important bits, and then skip back and wrap up in the present?
I feel flashbacks can be kind of shaky ground, because as you say it CAN feel like stalling - but sometimes, they can also be a very effective way of revealing secrets the character is keeping, etc. I also like the contrast of having the flashback show the true version of events, but then skip back to the present and show the character telling it in another way - i.e: revealing the truth to the reader, while the character still lies to the rest of the cast. It tells you something about the character and the nature of the secret, and stuff.
But let's see, what comics have I read that handle flashbacks well...
The Girl Who Flew Away - admittedly, these are less "flashbacks" and more "visions of someone else's life", but they're handled by having the main character dream scenes from a little girl's life at night. It's basically telling two parallell stories, which I assume will intersect at some point, and even though they have yet to intersect, they thematically play off each other.
Rickety Stitch and the Gelatinous Goo - each chapter of this begins with a dream or a memory in black and white of the main character's past life, that he in his waking life can't properly recall. Piece by piece, they're coming back to him, confusing him, and being the spark and the fuel for his continued quest. They're woven in as an integral part of the story, and become part of the hero's motivation, instead of just being info-dumps.
She Dwarf - Has had one flashback so far that took place as the main character passed out, and it was only a few pages long. In terms of pacing and plot, it was placed at precisely the right time.
Mare Internum - handles its flashbacks as Interludes between chapters, giving you relevant bits of the main character's backstory piece by piece, in short chunks. [warning: contains mentions of childhood sexual abuse].