Although I don't remember for certain, it seems like "Double Shock" ends in a similar way as "Dead Weight", with Columbo walking away with Mrs. Peck, though perhaps not trailing off in conversation as in the "Dead Weight" ending. Of course, "Dead Weight" has a memorable beginning, as well, if only for the fact that (I believe) it's the sole '70s episode where the credits appear in the opening.
Also, your mention of "Dead Weight" somehow reminded me of how playful the ending of "The Greenhouse Jungle" is, and while it may not be one of the most remarkable conclusions overall, I feel it has one of the best closing lines with Columbo saying, "My wife would kill me", referring to if he had forgotten the African violet. I like how it alludes to the whole business of Kathy Goodland having been made out to be a vindictive, even murderous wife throughout the course of the episode.

Upon reviewing "Double Shock's" ending again, I realized that it's really not very similar to "Dead Weight's" ending at all; somehow I had thought there was a conversation between Columbo and Mrs. Peck in a similar vein as his talk with Helen Stewart.
In regards to "Dead Weight", one aspect of the ending that really stands out to me is Hollister very sincerely telling Helen that he's sorry. One expects the murderer to be apologetic towards someone directly hurt by the crime that was committed ("Etude", "Death Lends A Hand"), but not toward a dispassionate witness to the crime, although, obviously, Helen became more than that.
Indeed, Hollister shows greater remorse toward having hurt Helen than Harold Van Wyck does toward his devoted wife of (presumably) several or more years in "Playback" (an episode with, I feel, an outstanding ending, as well).

re..dead weight...one of my LEAST fave episodes
an interesting story from Suzanne Pleshette

http://www.youtube.com/watch?v=k9qjn18ohR0

"The conspirators".

We discover where they hide the pistols at the end and the solution is nothing less than surprising !