Hi guys, I use my notebook as an amp and I've been using it with guitar rig and some other amp simulators. Even though there is no delay or lag,I can't say that the sound quality is satisfying and sustain doesn't last much,especially in the high E.I looked up to some topics in which some guys recommend using a sound card, but they did that mostly to guys who complain about delay/lag.So I was wondering whether a sound card will make a noticeable improvement in the sound quality,and if this is the case what are the cost efficient ones?
Your sound card has nothing to do with it. If you're using a proper interface, that replaces the sound card. If you aren't using a proper interface, you're doing it wrong.

Go to the Recordings forum & read the Interfaces Sticky.
Gibson LP Traditional, LP GT, LP Studio, SG Standard x2
Barber Tone Press > EHX Worm >TC Polytune > MXR Custom Badass 78 > EXH Glove > EHX East River Drive > Zoom G3 > TC Spark Mini Booster
Laney VC30
Marshall TSL602
Jet City JCA22H
My SoundCloud
I don't even know of or think there are sound cards you can put in a typical notebook. Using the sound port of a notebook is the least preferred method of all in capturing your sound.

Perhaps you mean a sound interface that works with USB or Firewire. That is the best approach, and is what Gary is referring to in his post. Around here you can get good ones in a Pawn Shop for $50+.