Check out the Sound Blaster X-Fi series and Asus Xonar cards. Do you game a lot or is it for music listening? Otherwise integrated sound chips in desktop motherboards are very good quality nowadays, so an upgrade might not be necessary as it was in the days of AC'97 chips.
Another option is to try to find Sound Blaster Audigy 2 ZS or Audigy 4 used. These are too solid sound cards.