I've had a few (and hope to have more).
The first was in 1979. I was taking a workshop in France. As I was walking around a small village, I came upon a scene which I wanted to photograph. I thought... I framed... I metered... I shot... That night, I processed the film, and printed the next morning. For the first time, what I saw in my head ended up on the paper exactly as I had planned.
Another occurred around 1983. I was on Cape Cod, where I had shot an image the year before, in color. On this trip, I wanted to duplicate the image in B/W, for hand-coloring. I had lugged the camera about a mile, it was over 100 degrees, and my eyes were stinging under the dark cloth. I got the shot, and packed up the camera, hoping to get back to the house for a cold one. As I turned, I saw a shot I thought would be nice but, being a puddle of sweat, initially thought about skipping it. A voice in my head said, "you'll regret it". I pulled the camera back out, set up the shot, and got it. To this day, I think of that moment every time I want to get to a cold one...