For music, 2.1 is all that is needed. Surround sound (5.1, etc.) is overkill since music pretty much all comes from up front (reverb is easily simulated and usually is mixed into recordings). It's not like the percussionist is going to sneak up behind you to try to kill you. By putting the same amount of money into a 2.1 system that you would have put into a surround, you will get much higher quality equipment.
The only advice I can give is stay away from Bose and Logitech. Logitech speakers do not hold up well and do not always give the best sound available in their price range. Bose makes great sounding, durable speakers but they are horribly overpriced for what you get (if you get lucky, you may be able to score a good used set for a reasonable price). The best advice I can give is to ignore the "experts" (keep in mind "ex" is a has been and "spurt" is a drip under pressure) and listen to speakers yourself. Don't be afraid to fool around with the settings. Everyone's ears are different and everyone has different tastes so the only way to ensure you will get what you will be happy with is to actually listen to them first and fine tune them to your tastes. What sounds like garbage to one person may sound heavenly to another one.
Keep in mind that the quality of sound from any speaker system, no matter how good, will be limited to the quality of the signal being fed to it. Except, possibly, for some of the most recent motherboards, onboard sound from a motherboard will severely restrict the quality of the music you will be able to hear through the better speakers. You will need an internal sound card or an external DAC to get the best quality.
The following rant will hopefully show why you need to listen to speakers for yourself rather that go by the advice of others.
Sadly, the best 2.1 computer speaker system I ever heard is no longer made: the Corsair SP2500. Corsair messed up when they marketed it as a gaming system. As a gaming system, it was mediocre since it was only 2.1. However, when paired with a good soundcard or DAC, its quality rivaled many larger and more expensive systems. Unfortunately, the early units were plagued with PSU problems, which hurt the reputation of the SP2500. Later units, such as the one I have been running almost 24/7 for a little over four years, were much better. I have my SP2500 paired with an ASUS Xonar Essence STX (that model has also been discontinued but a newer, supposedly better one is available) and the sound is better than that of any other system I've heard in the same price and size range.
What really killed the SP2500, though, were the audio snobs audiophiles audio snobs (I had it right the first time) who couldn't get it into their thick, opinionated skulls that such a compact system could actually sound good. I got into a pretty heated discussion over on another forum with the audio snobs who swore up and down about how bad the SP2500 would sound without having ever actually listened to it.
Even people who did have the SP2500 often complained that the bass was wimpy, even when told that it doesn't "sign on" unless you crank it, after which it can P.O. the neighbors and rattle windows. I repeatedly told one guy on that same forum you have to turn up the sub volume before you will hear it and, for some inexplicable reason, couldn't accept that advice until he finally did turn it up, then he was amazed by the sound. Audio snobs are just too hung up on their sacred cows to accept anything new and different.
. I had really started playing Hard Rock on them. I do watch movies on the PC but surround sound is not important to me, I prefer music. 
