I have two versions of the Sound Blaster Audigy 2 sound cards. One in my notebook and the other in my carputer. They provide reasonable sound for the price and include optical out + lots of nifty features. I have yet to fine tune the audio system for the carputer but after tweeking the notebook settings I have grown to love the card.

__________________
1983 Mercedes 300SD
1987 Mercedes 300SDL
2001 VW Passat 2.8 AWD
2007 OM642 Jeep WK 4x4