I was looking to do this a while ago and found the Pilot kit to be the best in terms of price versus performance. The ballasts are Japanese made so, at the better quality end of the spectrum, compared to the Korean and Chinese built ballasts. You should be looking for at least a 1 year warranty on the ballasts and bulbs but, some go from 2 years upwards. Also, the Bi-xenon kit is the most idea as, you'll have a HID dipped and main beam as opposed to just a HID dipped beam or HID dipped and halogen main beam. Again, the idea colour temperature is 4300k (the same as sunlight) but, 5000k kits are also very good. You should note that although one company may state they're kit is 6000k, it's probably more like 5000k. You can normally tell by looking at pictures on their websites.
As the kelvin scale goes up, the light output goes from white (4300k-6000k) to white with a blue tinge (6000k - 7000k) to blue and then through to purple at the 10000k -12000k end. These kits are for 'show' use only and completely non road legal, plus not having any usable light output.
The site mentioned above is the best in the UK but, if you scour fleabay, you can find some good suppliers in the states on there !
You should ideally be looking for a 'plug and play' kit. This will allow you to plug the ballast into the car harness via a supplied loom and then just put the bulbs in and plug them into the ballast. A 20 minute job on the R. Oh, and keep the ballasts out of places where water can get to them !
Hope that helps a little