I understand that not cluttering up the questions and answers with "thank yous" and "me toos" is important to ensure clarity and stay on topic. Indeed it is a great feature of this site. Is there an appropriate way of saying thank you to a particularly helpful editor/commentator/answerer?
The obvious way to say "Thank you" is with an up-vote!
When that isn't sufficient, a comment can be made, but most "Thank you" comments will eventually be deleted by moderators, as they don't really contribute to the long-term value of the site.
If you feel an answer really deserves an extra big "Thank You," you can also open a bounty on the question to award between 50 and 500 reputation to the deserving answer.