Bob, besides DDM there are a few other "brands" around, for example VVME. Here is their product page for the H7 slim HID retrofit kit
- 2 lamps and ballasts for a bit over $50. You may want to buy the set and split with someone - or just keep the other half as spare.
I am writing "brands" in quotes, because between all my bikes and my truck I must have 8 HID-retrofitted lights, installed within last 4 years. I have DDM, VVME and another one which I do not recall off-hand - and I believe that they are all made by the same manufacturer. Aside of stick-on labels, everything else - ballasts, ignitors and cables - are identical in appearance. I had one of the slim ballasts fail in late 2009 season (unreliable start) and I replaced the ballast with one from a possibly unrelated kit - no problems in 2010.
What I am trying to say is that I would not get hung up on brands, because very likely the stuff inside is all the same. Just get anything - Google search is your friend. The kits are so cheap that it does not pay to worry, it is easier to just replace what fails. Once you think about it, the $25-35 that a single set costs is often less than that of a "premium" halogen lightbulb.
To follow up on Andy's comments
: I personally stay with 35W kits because they are already very, very bright (do not forget that you are blinding oncoming traffic much more on a bouncing bike than in a car - also, you are retrofitting into a reflector shell which is designed with a different focus point, for halogen filaments) and that the 55W sets may be stressing the bulb more (not the bike).
There is a bit of confusion about ratings. 35W set generates 35W into the lamp. The inverter ("ballast") is not 100% efficient, in reality the power draw from the bike is in the low 40's - which of course is still less than the OEM halogens. This means that 35W kits are actually less of a load for the bike than the original halogen light.
Correspondingly, the 55W kits draw a bit more than the designed-in halogen current. However, we are talking here about a difference of some 500mA - it really is not a problem. The melt-down issues you are hearing about are coming from people who install 80W or 100W halogens - now, that makes a big difference in dissipation, and I would never do that.
The other issue is start-up current, which is quite high - but then, the spike on a cold halogen is also close to 6-10 times nominal. This means that start-up current does not matter as long as your connections are up to snuff, not loose and not oxidized - at that holds for both halogens and HID's.
Bottom line, from power draw and heating point of view, you could use either 35W or 55W kits.
My concern is with the blinding, mentioned above, and with longevity of the bulb. My understanding is that the lamps are the same for either power, it is the ballasts that differ, driving 35W or 55W, effectively overdriving the lamp for the higher power level. Nevertheless, I do not see reports of early failures on the motorcycling forums.
As another piece of trivia: while the ballast determines the power, the color is determined by coatings and gas composition in the lamp. That means that one could change the color by replacing the lamp, while leaving ballast in place.
Too much info?