Castiel's Hair
The variations in Castiel's hair through the seasons are not as noticeable as those in Sam's Hair, both because Sam's is longer and because Castiel's style is much more chaotic. It is a rough, fluffy, un-parted look. In his earliest appearances, his feathered coif was unpredictable. As Season 4 progressed, his hair settled into a pattern: longer and gelled back in front, spiked and pointing slightly forward at the sides. He returned in Season 5 after his first death with shorter, but no less variable, hair. It was usually swept up or back, sometimes spiked, sometimes with a slight curl. In Season 6, his hair was even shorter, and grew more orderly with time. When he ceased to be an angel in the season finale, his hair had never looked more precise.
Castiel's hair should not be confused with the hair of his vessel Jimmy, or that of his possible future self, both of whom have much flatter hair.