I have C-Media's 8738 onboard soundchip which came with my Elite P6BXT-A+ mobo - it is remarkably good and produces some splendid sounds from my £50 IBM 2.1 speakers.
I believe the 9738 is even better and again is very keenly priced.
Went into Dixons today (got a voucher as a birthday present) where the Creative Sound Blaster 4.1 (£25) and 5.1 (£30) retail versions were on offer.
Debated but felt I wouldn't improve much on the 8738, which is capable of rendering Eva Cassidy, Norah Jones etc in clean, crisp and transparent sounding stereo.
It also handles 3~D positional sounds very cleverly (there's a helicopter demonstration if you require) and has SPDF facilities.