An overhead bulb that is infrared will be fine, or a ceramic heat emitter (which is a special type of heat bulb)

Here are the two I would recommend:

infrared heat lamp:http://www.petsmart.com/product/inde...AvailInUS%2FNo

Ceramic Heat Emitter: http://www.petco.com/product/5003/Zo...-Emitters.aspx

You don't want to use a white bulb though.