Richard Cohen at WaPo writes this column, listing some of President Bush's flip-flops.
For my part, I would just as soon that the candidates stopped talking about flip-flops. It is such an asinine discussion; no one really wants a leader who won't change his or her mind upon realizing that he or she has made an error. The implication is that one candidate or the other is more likely to flop if the political winds shift. They call it flip-flopping.
I call it political accountability. Sometimes there is virtue in holding a position that your constituents don't hold; our distrust for rule by simple majority is why we elect representatives instead of governing by referendum. On the other hand, there are certainly situations where we want our political leaders to be responsive to the wishes of their constituents.
To my mind, the only time when it really makes sense to make an issue of a flip-flop is when the flip-flop involves some sort of deception. For instance, when President Bush was campaigning against Al Gore, he claimed to have supported a Patient's Bill of Rights as Texas governor. This is a patently false statement, since he vetoed the first version that the legislature passed and then allowed the second version to become law without his signature when the legislature passed it with a veto-proof majority.
That's about honesty. You don't get to take credit for the political achievements of others, particularly if you opposed their efforts.
Of course, as long as the media and the voters continue to fixate on whether an elected leader changed his mind, there will be a big incentive for that leader to frame every decision as "staying on course."