QUOTE (GBMike @ Apr 1 2011, 10:20 PM) Given that you've already had replacements installed from several different brands, it's time to focus on what's abusing them under the hood. Given that you don't mention any discoloration or other abnormality on the surface of the bulb, it sounds as though you are handling them properly during installation (NO fingers, right)? Material left behind by your fingers will create local hot spots on the bulb and will usually take a halogen lamp out very quickly. Actually, contamination from any source can be a problem. I assume that the seals on the housings themselves are keeping the elements out? No signs of fogging or water getting in there from your oh-so-salty Florida air? One of those two is usually the killer.
Another killer of halogen lamps is 'short cycling'. Did your lamps seem to be behaving normally in use (never any flickering while in use) before they stopped working? Was there ANY sign of corrosion on either the socket or the bulb when you removed the bad ones?
Alternately, and far more difficult to notice, is the reverse -- a situation where the headlights are being (barely) flickered [b]on by an intermittent connection through the multifunction switch or a defective headlight relay. Those can be a total bugger to spot since in the daytime, you'd normally never notice them flickering on from the driver's seat. Fortunately, that's really quite rare. Both conditions will take out the older sealed beam lamps as well.
Check all ground connections carefully. Then there's the old "check the voltage regulator output". Transients aren't usually an issue. It's a sustained overvoltage we're looking for, but that kind of problem will take out the battery and other incandescent lamps in short order, and the headlamps would be the least of your worries.