It's not a roller coaster, but Tower of Terror at DCA. It was around the time it opened, for some coca cola contest or something. But nobody was there, and we literally stayed on the ride for over an hour without having to exit and go through the queue. We rode it over 20 times before i stopped keeping count, and even after that we spent the last hour of the night riding it over and over again... so who knows how many times in a row it was. By far the most I've ever ridden a single ride in a row.
Now, if we're only talking roller coasters, than Goliath at SFMM still holds my record at 15 times.