I've had a couple of PIAA bulbs that came on parts bikes. They're pretty good and definitely better than stock.
However, since I added relays and beefed up the headlight wiring I like to run $8/bulb 100/90W Xenon bulbs I buy on Fleabay. They put out LOTS of light, enough to easily do 80 at night.
The first one I bought lasted about 35k miles in my LT under the low beam died.
Last summer, after about 20k of riding BOTH beams went out at the same time. When I pulled the bulb I discovered:
(http://i82.photobucket.com/albums/j246/smithduck/ChineseH4.jpg)
The one that replaced that lasted a whopping 7,000 miles. Rut roh. Oh well, what do you expect at that price and I still like them and will continue to use them. Since they're only $4 each I just carry a spare in my tail cowl.
WARNING: Don't run higher watt bulbs if you haven't beefed up the headlight wiring and added headlight relays (http://www.motobrick.com/index.php/topic,268.0.html). You'll most likely melt the insulation off of the stock wiring and the headlight wires aren't fused so you could be in for a world of hurt, maybe even a nice little bike fire.