Do you want surround sound? 5.1? 7.1?
Or would 2.1 do?
I have two sets of speakers. Attached to my iMac I have a set of white Aego M 2.1 speakers. They cost £120 so in the U.S. would approximately be about $200? Acoustic Energy are a hi-fi company and the build quality of the speakers is absolutely excellent. They have a three-way switch for the sub's bass level and a 3.5mm jack on the front for connecting an iPod etc.
And the sound quality is superb. They're definitely the best speakers I've owned- I'm no audiophile but read reviews online- there are plenty out there who agree with me.
My second speakers, attached to my Wii and HTPC, are the Logitech Z-5500's. These cost £230 so would be approximately $400-$450? They come with a remote, control station, the most outrageously large subwoofer ever and about 97 miles of speaker wire
The sound quality of these is very good indeed and they're very flexible and have good features. It's also worth noting they support DTS if you're watching movies. They also have connections for optical and coaxial if you want to connect other devices.
They are incredibly powerful- these are real room shaking. But with tinkering you can very good quality sound from them.
I would recommend either set to anyone. The Logitech's offer a little more "clutter" for just on a PC desk but obviously have the power and rear speakers. The Aego's are very minimalist and sound GREAT on my iMac.
If I remember rightly the iMac output doubles as a TOSLink connector for optical out too, so that's an option.
Hope this helps. If you want pictures of either, let me know- I'll dig out my camera
