I think the key is to NOT get internally amplified speakers.
You can get leaps & bounds above all cheapish computer speakers by buying a small reciever off craigslist and then get a beatiful pair of monitor / book shelf speakers.
You can get a terrific second-hand reciever/amplifier from someone who's retiring their equipment in the chase for 3D, latest HDMI processing,. etc. This gets you strong, honest amplification (more than just volume btw) and better DAC capabilities than integrated amp w/ speaker's I've seen.
On the subject of the speakers - note that bookshelf is just a form factor - the size might be right, BUT some book shelves might sound best a dozen feet away form the source.
Monitors on the other hand, are design to be listened to close up - which is what you want.
Do some homework - read up on reviews, etc. I would take a look at KEF. There are some discount places selling at huge dicounts and you can just barely get into KEF for $200 if you seek them out. They feature tech similair to the world class THIEL speakers that put the tweeter and mid in the same plane - which I think would help keep the sounding great.