Yes, I have a same problem on my Lexus. It was the same thing. You turn on the lights and some times left or right headlight is off. You reset the switch and lights working again.A month later I found out my left head light is never turn on, I checked and that appears - my bulb is explode inside. It's not a electrical problem, it's a light bulb! I replace 2 bulbs and have no problem ever since.
You need: D4S PHILIPS HID Bulb XenEco 42402. My dealership (Seattle) want 700$(!) for pair, but you can easily find them on the INTERNET for less than 100$ (make sure they OEM and Philips brand).
http://cgi.ebay.com/ebaymotors/ws/eBayISAPI.dll?ViewItem&item=230409580703&crlp=1_263602_263622&ff4=263602_263622&viewitem=&guid=126a0cda12b0a0814ad3a843fff50da5&rvr_id=140188752909&ua=WXI7&itemid=230409580703
Good luck my friend!