What you're seeing is a small speck of dust on the filter that sits over the image sensor. There are some easy ways to deal with it. The first and easiest way is to just photoshop it out of every image you take…yeah, not that fun.
Next up is to put your D80 into mirror lock-up mode (in the settings menu) and try to blow the speck off with a dust blower. Finally, if that doesn't work, you're going to use a specialized sensor cleaning swab to clean the filter (also in mirror lock-up mode).
Cleans delicate circuits and hard to reach places. — 50+ available at 7.95 each.