The two kits I looked at were the Morimoto 3Five system from theretrofitsource.com, and the XenonDepot Xtreme Digital kit from KBCarstuff.com.
I believe The Retrofit Source is based in Georgia, and KBCarstuff is based in Canada (outside Toronto I think).
There are lots of other kits available out there, but these two companies seem to have a pretty good reputation for solid customer service; that's why I narrowed it down to those two. I think pretty much all aftermarket kits are made in China, but I felt that I'd have a good chance of getting a problem taken care of with these two brands if one came up.
If you're looking for higher quality hardware, you'd probably have to go with parts from an OEM supplier. This would require a little bit more work when installing and the parts would very likely cost a lot more.
There's tons of info on HID upgrades on the HID Planet forums. Probably much more than you'd ever like to know

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