Mary T's 200 fly is #2 on my list. These swims were generations ahead of their time.
Sometimes a swimmer will put up a new time that shows everyone else what is possible, but these swims were just so unbelievable that it took ages for other swimmers to even seriously challenge them.
Addendum: Actually, the current women's 200 LCM fly record is also such a swim. It's a shame that it is widely considered suspect.
