Our annual trip to Kingston SE on the South East coast of South Australia. If the wind isn't on shore for the 100km odd beach, you can always go to the claypan which is a dry lake about 1km wide and 4km long. This year there was some water on it in places but the wind can push all the water over to one side of the lake overnight. Most of the time it was dry enough to buggy on.
March 2011, the Extreme Kites Labor Day meet down at Sandy Point, located 2 south east of Melbourne, Australia. The beach can be around 100m wide at low tide and 14km long. And usually really smooth too.
At the end of the Kingston SE 2014 trip, Rob, Cris, Mark and myself spent a few days at Narrawong, 15 minutes east of Portland, Vic. 15 minutes on the west side of Portland is the beautiful beach at Cape Bridgewater. Very wide and flat, but you wouldn't want to buggy when it's busy. This was just after the holidays.