i know a few speaker brands but i'm not a walking encyclopedia of them. you may want to do a bit of your own research such as reading threads like this
http://www.avsforum.com/forum/89-speakers/1455780-basic-set-bookshelf-speakers-under-200-a.html
perhaps this for $180
http://www.newegg.com/Product/Product.aspx?Item=N82E16882325059 paired up with a $100 amp
http://www.parts-express.com/lepai-lp7498e-200w-class-d-digital-amplifier-with-bluetooth-and-power-supply--310-298 although going with a better quality amp then a lepai may be beneficial since they often get higher %thd when you start cranking the volume up near max and often arent quite capable of the power ratings they claim. still, they have cheap amps which work decent for the price.
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personally i use a set of klipsch satelite speakers (klipsch quintet iv 5.0 set) with a 450w subwoofer (sw-450) with a pioneer receiver (vsx-30). pics in signature under "build". i love my klipsch speakers and they sound great but i didnt have the money for a full blown surround sound set if i went with the bookshelves.
i've heard the floorstanders and bookshelves in the store though and they definitely DO sound nice if you like their particular sound. klipsch tends to be a bit brighter in the bookshelf speaker size then others so some might not like this but if you do then
http://www.amazon.com/Klipsch-KB-15-4-Inch-Bookshelf-Speakers/dp/B00AS3X740/ref=sr_1_3?ie=UTF8&qid=1408286456&sr=8-3&keywords=klipsch+bookshelf may be something worth considering. you can go down to your local best buy or audio shop to listen to some speakers which is what i would highly suggest doing!.
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normally i would just say to use a stereo receiver to power them however since you already have a high end soundcard and want to use it... really the only way to do that would be an amplifier (since receivers typically take digital input only nowdays) so using a receiver would bypass your soundcard.
however, also of note would be that if you used your soundcard out of the 3.5mm jacks you would be double-amping which may reduce sound quality a bit. so, perhaps it would be an option to use the optical jack out of your soundcard along with a 2.0 channel stereo receiver with 100w x channel? this should allow you to use any sound processing on your soundcard but not doubleamp.
another wayt to do this would be to use the "line out" port on a soundcard which is not amplified and since you only want a 2.0 set this would be perfectly fine.
also of note is that getting a better amplifier then the lepai listed above for $100 is going to be very hard. you may find some pyle stereo amps which might be a hair better but anything from a more respectable company tends to be a bit high dollar. just a thought, not to say that these amps will not work just that they arent going to be capable of turning the volume up to very high levels without some distortion (and by that i mean house-party or concert levels and not just normal listening levels).