General Aftermarked HID headlight housings:

Hella 90 and 120mm

Generic sealed beam HID housings:

1970-1990 model cars with 6054, 6024, 4656, 5006 "sealed beam" headlights in various standard sizes can enjoy new complete HID headlights from Sylvania. They are even legal.
Note that the X6024 model has some unfortunate properties: 3 hot spots, one big oval in the center, and one on each side. Light is not evenly spread. The output is not much brighter than you can achieve from a high quality 6024 headlight from Cibie or Hella. See redhummer.com for details.

Specific car model HID housings:
 

Years:	Brand:	Model:	Manufacturer:	Low Beam Optical method:	Light Output Quality (1-5):	Other:
1992-99	BMW	3 series (E36)	Hella	projector	5	ECE version. Comes with auto levelling and angel eyes (Celis). Hella P/N 1AL 008 875-821
98+	Ford	F-150	Sylvania	projector	?
1999-	Ford	Focus	Hella	projector	5	Uses the well know Hella 90mm units. Orderable also in Halogen H7 versions: BAT Inc, USD 549 (May 2002)
1999-	Ford	Focus	Vmaxx	projector	-	Should be great as a basis for HID projectors. Price: 460 Euro. See details under Chrysler Voyager.
99+	Chevy	Trucks	Sylvania	reflector	-	-
2001-	Chrysler	PT Cruiser	Vmaxx	Projector	Should be great as a basis for HID projectors.	Details as Chrysler Voyager from Vmaxx.
1995-2001	Chrysler	Voyager (Euro Caravan)	Michalak Design	Projector	-	Direct link. Available in silver and black. Transparent front glass seems to be a cover only. Price ~1000Euro. Should be great as a basis for HID projectors.
1995-2001	Chrysler	Voyager (Euro Caravan)	Vmaxx	Projector	-	Utilizes Hella halogen 90mm high, low beam and turn light modules. Price: 761 Euros. A cost saving solution is to buy Bezel and mounting hardware separate from vestatec for 130 Euros. Use your own wiring harness and hella units of choice. Helps if you speak German, but if you are lucky you might get in contact with english speaking staff. If not the Altavista Translator will get you by. Should be great as a basis for HID projectors.
1996-2003	Chrysler	Voyager (Euro Caravan)	Vmaxx	Projector	?	Details as Chrysler Voyager from Vmaxx. Price: 768 Euros Should be great as a basis for HID projectors.
2002-2004	Subaru	WRX	Hella	projector	5	Comes with H7 Hella 90mm units. Good basis for HID upgrades of various kinds. Link to seller: 1
1999.5-	Audi	A4	Valeo	projector	5	1
	VW	Golf IV	Bosch	projector	5	Sold as an aftermarked product in North America. Sold as a factory option in ECE countries. Picture1 Picture2
	VW	Golf IV	Hella	projector	5	Goes under the name: Triple round. It uses Hella 90mm low and high beam modules. Here is a disassembled picture (933k).
	VW	Bora/Jetta IV	Bosch	projector	Assuming 5	1
	VW	Passat B5	Hella	projector	Assuming 5	1
	VW	Passat B5.5	Hella	projector	Assuming 5	Bi-Xenon
-1999	Mazda	Miata	Hella	projector	5	http://www.midtennmiata.com/: Assembly based on DOT HID Hella 90mm low beam and H9 high beam - price from USD 399 + HID hardware. Detailed Information Note the outboard mounted high beam module. That would not conform with current DOT regulations.
1993+	Mazda	RX-7	Hella	projector	5	Rotaryextreme.com: Assembly based on DOT HID Hella 90mm low beam and H9 high beam - price from USD 1450. Sale sheet Install sheet Note the "human skull" pattern above cutoff on the Sale Sheet. That would probably not conform with current DOT regulations. Its probably a reflection from the carbon molded sheet right in front of headlights. This area should rather be painted flat black.
90-96	Nissan	300ZX	OEM Nissan	projector	Assuming 5	Link

Where can I ask questions?

Please visit the online forum. There are plenty of people that have automotive lighting as a hobby and are willing to help you.