Depends on what kind of audio/video editing? Professional/Studio, family stuff. Mid range?
For the family stuff if you have a reasonably new pc your pc should have a AC'97 onboard sound. Which is fair alright to my non audiophile ears.
However if your doing more upmarket stuff any of the Creative cards are usually a fair go. Something like the Creative X-Fi Xtreme would do the trick easily. $50 from Umart.
Umart Online
If your doing professional stuff, I would suggest checking some review sites for truly high quality sound production gear