Sometimes suggestions from comments get incorporated into the accepted answer. In such scenario it is common to mention the commenter who provided some useful input. Usually such mention is in a form "as @nickname suggested" or "from @joes answer" etc. Could that be a good idea to add a new functionality to the Stack Overflow engine to credit those who have provided some useful input to your answer?
I was thinking along the lines of allowing you to choose the from the names of the commenters in a way you choose from tags, and then displaying the selected names somewhere under the answer as we already display the name of the answer author and the name of the last person who edited it.
Imagining even further I can envision Stack Overflow giving some reputation points to the contributors, maybe deducting from the original author or just giving some extra points. Maybe like 1 point for 5 upvotes or something along those lines. Those are just random numbers of course, you need to carefully think how much reputation the contributors should receive if this idea ever gains anyone's attention.
I think this form of a contribution from comments (or other answers) is a great part of the Stack Overflow society already. Think about it, if a commenter knows that his comment might be referred in the answer with a possible reputation gain, this might motivate people to give better comments.
Also the author filtering out only those comments that he thinks have really contributed to make the answer better is another way to praise the commenter than the already existing comment upvote button very useful by the way. Thinking about it, I even imaging the original author of the accepted answer selecting the particular comment and then this comment being marked with a special icon or other outstanding visuals so that the audience can see the good comment and also, which I think is important, seeing such contributions marked can be a good model for the audience to follow and provide better comments.
Also thinking even more about it I can think of authors whose answers are not accepted but are linked as contributions to the accepted answer motivating many discouraged people who want to contribute but do not get many answers accepted due to competition. Of course they should have commented instead, but we know that too many posts become answers because of competition rather than becoming comments. This is a nature of a competition versus collaboration model we have here which is exciting. I think that both competition and collaboration can win here.