Use energy-efficient light bulbs if you're looking to cut as much energy costs as possible. The socket on this bulb is a so-called GX24d-3 socket.
From Amazon
Osram DULUX T 26 W/840 Plus 26 Watt 2 pin Compact Fluorescent Light Dulux T/E Plus Cool White (4000k) Lamp
LED Bulbs
Osram Dulux 26W PL-T Plus 2PIN Cool White - 342047
Big on Electricals
Osram Dulux 26W PL-T Plus 2PIN Cool White - 342047