Low Beam HID
 

I just installed these in my 2005 XK8. They are bright enough and show as white (not yellow). After installing my fog lamps now have a yellowish tint as compared to the headlamps. You cant beat the price for (2) bulbs.

Camden D1S OEM Grade HID Replacement Bulbs Pair 43K 4300K White Xenon Error Free | eBay

The Advanced Auto equivalent is $99 ea bulb. This is a top rated seller. Shipping is free and I received mine in roughly 4 days from time of order (USA).