Most balancing rocks occur as a result of being deposited by glaciers or eroded by wind and water. Some of the more impressive ones are:
North Salem NY. Photo is undated.
Pittsfield MA. Photos are undated.
Twin Falls ID. Forty tons of rock balancing on a 3 foot 17 inch base! Photo is dated 1937.
Camden ME. First photo is dated 1889. Second is undated.