Andy,
I *almost* always drive the back light with a separate pin via a MOSFET to have the option of PWM dimming of the light. If you have 2 pins to spare - 1 for LCD and 1 for BL. Many LCDs draw so little power that you can direct drive the LCD from an I/O pin. Check the power specs of your particular LCD or just use a MOSFET. My preferred MOSFET is the 2N7000 for up to 200mA or the BS170 for up to 500mA.