In Lego Harry Potter: Years 1-4 for PS3, Xbox 360, and Wii, one of my favorite unlockables is the Stud Magnet effect which gravitates studs to you from a much greater distance.
To unlock Stud Magnet the easy way, go to Wiseacres Wizarding Supplies in Diagon Alley and visit the vendor upstairs and put in the code 67FKWZ.