Over the Gulf of Arabia in August, we had a good rollercoaster for a very good portion of the flight. All service suspended and any crew who were up and about the cabin were being held down by pax or holding onto the under seat struts. According to the IFE maps we were dropping hundreds of feet at a time, then climbing again then dropping, you could hear the engines doing that "roar" they seem to do in bad turbulence. The cc said it was some of the worst they had ever encountered. On arrival at LHR several pax did "a pope" and kissed the floor. It was very, very hairy.
My favourite ride is SFO/RNO as you crest the Sierras the ride is always very bumpy due to the sudden updrafts from the desert. The first time you do the flight it's scary, but once you know what's coming it's good fun.