You would need a full HID kit to turn your fogs into Xenons. You can get Xenon-match bulbs to match the color of your Xenon headlights, but they will still have the illumination of typical Halogen bulbs. If you want Xenon-match bulbs, I'd say go with a set of Philips BlueVision bulbs, or if you just want a good pair of regular fog light bulbs (non-Xenon-match), go with a set of Philips Premium bulbs. Ultimately, the bulbs you get are up to you; you just need 9006 bulbs, or also referred to as HB4.
You can get Euro-spec versions (which are brighter than US-spec bulbs) of the Philips bulbs listed above at
Http://www.powerbulbs.com/. The cheap solution would be to pickup a pair of brand-new bulbs off eBay.