If I ask a question that nobody else is able to answer, and I later figure it out, then there is no way for me to mark the question as answered. It will be marked unaccepted forever. I consider this to be a bug since it'll have a negative impact on statistics, etc.
You can answer your own question and then mark it as the best answer after two days of asking the question. It won't be considered as an unanswered question if there is at least one upvote on the provided answer. There is even a badge promoting such a behavior.
But there is a way!! Write your own answer, and then accept it.
it isn't considered impolite.
it gets off the unanswered list.
For more info, take a look at this meta stackoverflow question.