PIAA 510 gets the job done... unless you're motivated to drop serious bucks for whatever reason. Simple, effective, inexpensive, and bulbs are available at any auto parts store. I inherited a set on my current ride and thought at first that they were merely decoration. Then I figured out that the beams weren't adjusted properly and the previous owner had put low wattage bulbs in to reduce the the draw. I switched back to standard 55w bulbs and adjusted the beams according to PIAA instructions and found that they're quite effective. They throw nice, normal-colored halogen driving light beam down the road well ahead of the high beam.
My experience is that they're more useful than much brighter driving lights. I once had a bike with PIAA 910s and 110w bulbs in each light. They would absolutely light up the night, but when meeting traffic I had to switch them off and I'd go instantly from the 910s plus high beam (had them wired to the high beam) down to low beam only. Since my eyes would be adjusted to the extremely bright light I'd be almost blind until my eyes readjusted. So for use on the highway I'd suggest thinking in relative terms to the bike's high and low beam output when selecting driving lights.