This energy-efficient light bulb is perfect if you're trying to keep energy costs down. The socket on this bulb is a so-called G24d-2 socket.
From Amazon
Osram G24d 18 Watt Compact Fluorescent Light Dulux Lamp
OnBuy
Osram Dulux D G24d-2 Compact Fluorescent Lamp 18W / 827 Warm