K12 JobSpot is a site that has listings of open teaching positions around the country. I did a little bit of searching on it and found quite a few positions out there.
It is easy to use and you can search by keyword, location, and job type. It does have a good number of teaching positions listed, but I was able to find more through a local agency and my teaching union site. I'm guessing that a lot of districts don't know about the site yet, so they haven't listed their vacancies on it.