Klipsch ProMedia 2.1- If you want to "Feel" Bass this is it, Very loud and has a good balance of overall sound after you knock the bass down many notches.
Harman Kardon Soundsticks III- Not as Loud and Bass is far from the Klipsch but they have a warmth and balance to them, I don't particularity like the way they look but they sound fantastic.
Logitech Multimedia Speaker System Z533- Very balanced and good quality, the bass and volume are weaker than the first two but it's enough to fill a decent sized room comfortable. Very good option for $80 one of the best you will find and they don't disappoint at all.
As far as addon sound cards I would suggest you try what you have first with the speakers you wish to buy and go from there...