The Muslim's Haircut 101

Men
Males may shave their hair or cut it evenly. That means, "GQ slopes", skip levels are not permissible. The length of the hair should be arranged so that they look smooth, and if there are any changes in length, the transitions must be gradual. Punk-Mohican hairstyles are not permissible. The best hairstyle is the Prophet Muhammad SAW's hairstyle. The hair should be combed back, and the hair is then cut in a straight line from the bottom of the right earlobes to the left earlobes horizontally. It is also sunnah for men to have the hair at equal end-lengths to down to the neck or the shoulders, though this may not be agreeable to employment requirements of today.

Women
It is not permissible for females to cut their hair for the sake of beauty or convenience. For dire health reasons, it is permissible. This ruling is observed even during the Hajj ritual of khuluq. During this Hajj ritual for men, shaving of the head is commended. But for women, only a portion of her hair is removed (approx. one centimetre). Thus it is understood here that a woman's hair should be long and even during the Khuluq ritual in Hajj - this is not sacrificed.

General
It is not permissible to adopt any hair style attributed to Non-Muslims and other religions e.g. monks, priests, punk, jews etc.