What I use at home and at work are the Klipsch ProMedia powered sat/sub combo. You just connect it to your computer via the audio out and adjust the volume through the left speaker knob or iTunes. I was able to buy these for under a $100 per set, but I think they have been discontinued.
If you want to spend a little more for better performance consider the NHT powered PC speakers.
http://nhthifi.com/current/products/pchifi/m00.html
Good luck!
If you want to spend a little more for better performance consider the NHT powered PC speakers.
http://nhthifi.com/current/products/pchifi/m00.html
Good luck!