Here’s a useful list of chipsets (found on motherboards) that are documented. Since it’s documented, it’s easy to add support for them & the drivers are less buggy.

If you really care about Open Source, contact the company & ask for hardware documentation/datasheets. We don’t want source code: we want freely available specs.

(Signing an NDA is not an option, we also want to share what we know to other groups out there: *BSD, Linux, Haiku, Minix3 and many other groups in pure open source spirit)

Intel:

ICH7
ICH8 mobile
ICH9

ICH10
CMD/Silicon Image
CMD 648
CMD 649
SiI 680
Promise:
PDC20579
PDC40775

ATI:
IXP700/800 SATA
Ethernet:

Realtek

Intel (complex and buggy)
Wifi:

Ralink

Realtek (older chipsets like 8187)
Video Adapters:

Intel

ATI

Soundcards:

Realtek
(Still a work-in-progress)