Do any clones refuse Order 66?
There's no evidence within the main film and TV canon of a clone trooper disobeying Order 66 (due to the fact that they were implanted with an "inhibitor chip" guaranteeing their loyalty).
Probably the closest we get is in the Clone Wars TV series where we meet a deserting Clone named Cut Lawquane. Since he's hiding from the Empire and supports the Jedi, I think we can reasonably assume that his chip is already damaged in some fashion and that he would have refused Order 66 if he received it.
Elsewhere in the book EU, we see in Dark Lord : The Rise of Darth Vader that not all of the clones obeyed Order 66. An entire squad went rogue due to their affection and personal loyalty to their Jedi general
“Word has reached me,” Palpatine was saying, “that a group of clone troopers on Murkhana may have deliberately refused to comply with Order Sixty-Six.”
Vader tightened his hold on the lightsaber. “I had not heard, Master.”
He knew that Order Sixty-Six had not been hardwired into the clones by the Kaminoans who had grown them. Rather, the troopers-the commanders, especially-had been programmed to demonstrate unfailing loyalty to the Supreme Chancellor, in his role as Commander in Chief of the Grand Army of the Republic. And so when the Jedi had revealed their seditious plans, they had become a threat to Palpatine, and had been sentenced to death.
On myriad worlds Order 66 had been executed without misfortune-on Mygeeto, Saleucami, Felucia, and many others. Taken by surprise, thousands of Jedi had been assassinated by troopers who had for three years answered almost exclusively to them. A few Jedi were known to have escaped death by dint of superior skill or accident. But on Murkhana, apparently unique events had played out; events that were potentially more dangerous to the Empire than the few Jedi who had survived.
“What was the cause of the troopers’ insubordination, Master?” Vader asked.
“Contagion.” Palpatine sneered. “Contagion brought about by fighting alongside the Jedi for so many years. Clone or otherwise, there is only so much a being can be programmed to do. Sooner or later even a lowly trooper will become the sum of his experiences.”
In Battlefront 2, the narrator (an officer of the 501st) displays doubt or at least some level of sympathy for the Jedi when talking about Aayla Secura and their experiences together on Felucia. He admires her skill in combat and says something along the lines of "when Order 66 happens, I hope she experiences a swift death." Not necessarily disobedience, but he shows some level of compassion for the Jedi that he knows he will wind up executing some day.
But... weren't the clones forced to follow Order 66 via the biochips implanted in their heads?
@AlfredoHernández - This is a case where a book contradicts a game. Which do you consider to be more canonical?
@Richard I was talking about the Clone Wars series, which is cannon as far as I'm concerned. Also, the EU books are not considered cannon anymore, right?
@AlfredoHernández - They're considered to be part of the "Star Wars Legends" canon. Higher than fan fiction, lower than the films and novelisations.
@Richard "Past tales of the Expanded Universe will be printed under the Star Wars Legends banner, and a new continuity has been established that consists only of the original six films, the Star Wars: The Clone Wars television series and film, and all future material from that point onward. Though past elements of the Expanded Universe have been declared non-canon as a whole, they remain a resource for future Star Wars material to reference elements of the EU, thus bringing these elements into the new continuity as canon." That means biochips are the only canon explanation of Order 66.