HIR bulbs are a good improvement, search ebay for "HIR" or go to www.rallylights.com and look under bulbs.

Another way to get a slight increase in light output is to do a 9005 "conversion", 9005 bulbs are your high beams and run at a slightly higher wattage than your 9006 low beams. There is a slight modification to the base and connector of the bulbs that needs to be done, but its very simple and im sure the instructions can be found on this forum somewhere.

As for aftermarket bulbs, what he said ^^

And why are you mentioning OEM replacement headlights? Are your headlights damaged or something?