Personally, I'd recommend these. Incredible bang for your buck. http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-...

You'll need an amp. http://www.parts-express.com/pe/showdetl.cfm?partnumber=300-...

To run from the headphone port you'd just use a simple male 3.5mm male to RCA(red/white) male.

I imagine the headphone port quality is terrible and the post mentions it. Apparently this is a cheap USB compatible option http://www.meritline.com/usb-sound-adapter-channel-volume-co...

This entire setup should run you well under $100 and sound great.

I run this exact setup in my home office and it's great.

I've been wanting to try the Topping amps; this one with an integrated USB DAC looks interesting: http://www.parts-express.com/pe/showdetl.cfm?partnumber=310-...

I use this setup in my living room. I don't think you could hope for more for the money. That little amp is powerful and can even run on AA batteries (8 of them).

Audioengine A2: http://audioengineusa.com/Store/Audioengine-A2

Or A5+ for a bigger sound at a higher prize and in a bigger box.

I have used M-Audio AV 40s, and have liked the results. They're compact, well built, and sound good.

Amazon link, no affiliate: http://www.amazon.com/M-Audio-Studiophile-Powered-Monitor-Sp...

Am i right in thinking that all usb speakers have their own sound card on board? I have a pair of logitech z120 I want to try out with this (and then maybe hook it all up to a battery to make it completely wireless) but i've left them at uni and can't try it out yet.

Yes, the signal over USB is digital, and the speakers have a DAC and an amplifier.

Look at the Pro Audio USB Monitor space - Alesis and Samson have good sounding powered nearfield speakers that are cheap by audiophile standards.

edit Samson not Samsung