Sound/audio card manufactures

Some of the most common manufactures of soundcards.

Creative Labs -> Support section
Realtek -> Support section
C-Media -> Support section
SoundMAX -> Support section
VIA(Vinyl) -> Support section
SigmaTel -> Support section
SiS -> Support page
Intel -> Support section
Avance(out of business) -> Support section(Not official)
Conexant -> No support section known, drivers from Realtek/Intel and probably others are said to be functioning substitutes.

See related article on how to find out what sound card you have.