I am relatively new to SO and see this very often. As the title suggests there are many questions that are answered in comments itself and they remain unanswered forever. Shouldn't there be an option to mark a comment as an answer and the comment is copied over as an answer or something like that?
I guess there should be an option to the creator of the question to do this.
There is absolutely no need for a feature that allows you to mark a comment as an answer. In fact, that goes against one of the primary tenants of the site: questions and answers are the primary focus, while comments are just "noise".
The better solution is to simply leave an @username reply for that person, informing them that their comment actually answered your question and requesting that they post it as an answer so that you can accept it. I've seen this done numerous times (and had people do it with me), and my experience has been that users are more than happy to oblige.
If (and only if) they don't come back and post their comment as an answer within a reasonable frame of time (say, a few days) should you consider posting your own answer to the question, as Mike suggests.
Very closely related...
How to Give Credit for An Answer in the Comments
As an FYI, you can always answer your own question
If I come across this and it's a question that's not mine, I answer in Community Wiki and give credit to the person who answered it in comments. If it were my question, I would post an answer and probably wouldn't make it CW.
