You would think Tackle would be one of the overused moves. The only overuse of Tackle is by Ash's Charizard...
Hyper Beam.... WHY DOES KINGLER KNOW HYPER BEAM?
Ice Beam.... Holy cheese at least 5 character Pokemon know Ice Beam (Lapras, Glalie, Buneary, Swinub (...), Dewgong, even Misty's Luvdisc used Ice Beam...)
Quick Attack, no discussion.
Flamethrower, also no discussion, at least 3 of ASH's Pokemon use it.
Iron Tail has become the cool move now and everyone should use it.
Water Gun I think would be the most overused move in the entire series simply because of MISTY!!!! As well as Ash, Dawn, May, heck even Brock has two that use Water Gun.