I had Tule River in Porterville California install the HID Landing & Taxi lights in my P337. Called the "Boom Beam", they offer this under an agreement from LoPresti.
They cost about $1,200 each (total for both ~ $2,400). There are 3 beam widths; I chose wide (55 degrees) for the taxi and narrow (10 degrees) for the landing. If you plan to only change out the landing light, there's a 17 degree lamp.
These lights have a 5,000 life - so for improved recognition, I just leave the taxi light on for most of my flights. Another (perhaps less important) benefit is that these draw less than half the amps as the original lights.
When landing at night, there is a very noticeable improvement using these lights. They claim they're 5 times brighter - but I'm not able to quantify the improvement other than to say they are definitely brighter. As Richard said, they are worth every penny (even if I did pay full retail). If you're on a budget, consider just replacing the landing light (and leave the taxi light the old style).
See their website for a nice write up about this system. Click "Products/LoPresti/Boom Beam":
http://www.tuleriveraero.com/