Back in the summer I was camping at a racetrack for a week and we were listening to music and watching DVDs on my laptop and was wanting more sound than the laptop was putting out. So I went to the local WalMart and found an Altec Lansing BX 1121 powered speaker set for only $30 and figured if I didn't like them much I'd just take them back to my local WM when I got home. I ended up keeping them - they sounded so damn good.
It's got two speakers and a down-firing sub cube that put out a LOT of full-range sound with impressively tight, deep bass and crisp, clean, airy highs - I was
very pleasantly surprised and the my fellow campers were impressed with the sound quality as well. I use them now when I watch movies on my laptop from Netflix's "watch now" service.
Not sure if it would be an improvement over what you have - but for only $30 you can't go wrong - and if you don't like 'em take 'em back to WM.