How to change the default text of Cancel Button which appears in the UISearchBar +iPhone

Use the appearance proxy:

id barButtonAppearanceInSearchBar = [UIBarButtonItem appearanceWhenContainedIn:[UISearchBar class], nil];

[barButtonAppearanceInSearchBar setBackgroundImage:grayBackgroundImage forState:UIControlStateNormal barMetrics:UIBarMetricsDefault];
[barButtonAppearanceInSearchBar setTitleTextAttributes:@{
                                      NSFontAttributeName : [UIFont fontWithName:@"HelveticaNeue-CondensedBold" size:20],
                                 NSForegroundColorAttributeName : [UIColor blackColor]
     } forState:UIControlStateNormal];
[barButtonAppearanceInSearchBar setTitle:@"X"];

You also need to have the "searchBar setShowsCancelButton" before the procedure.

- (void)searchDisplayControllerWillBeginSearch:(UISearchDisplayController *)controller
{
    [theSearchBar setShowsCancelButton:YES animated:NO];
    for (UIView *subView in theSearchBar.subviews){
        if([subView isKindOfClass:[UIButton class]]){
            [(UIButton*)subView setTitle:@"Done" forState:UIControlStateNormal];
        }
    }
}

Note also: use UIButton to avoid problems with Apple!

Solution for iOS 7. All credits for this go to Mr. Jesper Nielsen - he wrote the code.

-(void)searchDisplayControllerDidBeginSearch:(UISearchDisplayController *)controller {
    UIButton *cancelButton;
    UIView *topView = theSearchBar.subviews[0];
    for (UIView *subView in topView.subviews) {
        if ([subView isKindOfClass:NSClassFromString(@"UINavigationButton")]) {
            cancelButton = (UIButton*)subView;
        }
    }
    if (cancelButton) {
        [cancelButton setTitle:@"YourTitle" forState:UIControlStateNormal];
    }

}