Attribute::Property is very elegant and simple. I like it mainly because it adds so little typing, instead using Perl's attributes to make any sub a property (accessor).
package Automobile;
sub new : New;
sub colour : Property;
sub owner : Property { /^(?:Jack|Jill|Bob)$/ }
package main;
my $car = Automobile->new(colour => "red");
print $car->colour; # red
$car->colour = "blue";
print $car->colour; # blue
my $other_car = Automobile->new(owner => "Jack"); # works
my $another_car = Automobile->new(owner => "Dad"); # fails
