IIRC, the fog lights take H3 bulbs. If you're looking for brighter fogs/using them as driving lights, there's quite a few options for halogens. Then you could always replace the housing and wiring and go HIDs. Or get a set of driving lights, like Hellas or something.
92 XJ - 7''/SeriousOffroad long arms/Bilstein 5100/Aussie/33x12.50 15x8 Kumho KL71s/plus more
98 5.9 -Monstaliner bed liner exterior - 3'' Kolak exhuast - SCT Tuner - OEM rubber cup holder insert - 52mm Holley TB - Complete audio upgrade