UITextfield leftView/rightView padding on iOS7

A much simpler solution, which takes advantage of contentMode:

    arrow = [[UIImageView alloc] initWithImage:[UIImage imageNamed:@"down_arrow"]];
    arrow.frame = CGRectMake(0.0, 0.0, arrow.image.size.width+10.0, arrow.image.size.height);
    arrow.contentMode = UIViewContentModeCenter;

    textField.rightView = arrow;
    textField.rightViewMode = UITextFieldViewModeAlways;

In Swift 3,

    let arrow = UIImageView(image: UIImage(named: "arrowDrop"))
    if let size = arrow.image?.size {
        arrow.frame = CGRect(x: 0.0, y: 0.0, width: size.width + 10.0, height: size.height)
    }
    arrow.contentMode = UIViewContentMode.center
    self.textField.rightView = arrow
    self.textField.rightViewMode = UITextFieldViewMode.always