Yeah, they don't exactly give them away, do they?  You'll get a lot of strong opinions with this question.  From what I've read, those who've taken the inexpensive route seem to prefer Naxos or Sylvania Silverstar bulbs.  They are direct replacements for factory halogens, meaning they operate on direct 12V and therefore do not require a ballast/igniter.  However, many argue that these produce a light that, while better than typical halogens, is not a true white compared to HID's.  They are a lot less expensive, though.  You can find them for around $30 a pair online.

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