The best deal money can buy right now is Logitech z-5500 5.1
Many people in this forum have these speakers, including me. I'm sure all of the owners will tell you they are very happy with them. Not only can yo use them for a computer, you can also use them with (CONSOLES) as well and (CABLE or SAT. TV)
Hurry buy them now at zipzoomfly.com $212.00 is the lowest you'll ever get on this speaker system.
I paid almost $300 for mine 6 months ago.
Some might say that the Klipsch ProMedia Ultra 5.1 are better, but it's all subjective.