Horseman press release:

Direct Source Marketing (DSM), the sole U.S. distributor of Horseman photo products for professionals and high-end consumers, today announced unique multi-coated conversion lenses for DSLR cameras. [Of course they should work on any film body, too. — ed]
"What makes the Horseman lenses unique is that they provide wide-angle and macro photography easily and [...]

The title pretty much says it all! More info: Web page, PDF data sheet, and PDF user manual.

Lensbabies launches the new Lensbaby accessory lenses, a Lensbaby Wide Angle/Macro Conversion Lens and a Lensbaby Wide Angle/Telephoto Lens kit. Most notable about the new wide angle accessory lens is that it is optimized for use with the Lensbaby – no other wide angle accessory on the market preserves the size of the sweet spot [...]

Trask Bedortha has been playing with flipping and mixing lens elements to get distortion-free wider-angle coverage. Check out the examples and descriptions in this thread in the Through the Viewfinder group (where you shoot the ground glass of another camera) on Flickr.

Carl Zeiss AG Press Release:

Oberkochen, August 15, 2006. The Zeiss Ikon SW is the 35mm precision camera for uncompromising superwide photographers. Its lens mount takes any lens with M bayonet, in particular the ZEISS high performance superwide-angle lenses Distagon T* 2,8/15mm ZM and the Biogon T* types from the ZEISS ZM range. An accessory shoe [...]

Direct Source Marketing (DSM) Press Release:

CONCORD, CA, June 22, 2006 – A joint venture between Rolleiflex and Horseman today announced one of the widest angle cameras on the market, Horseman SW-D Pro, which accepts digital camera backs to give professional and high-end consumer photographers wide angle opportunities that weren’t available in the past for [...]