Hi rh6, I agree USB speakers are very good for people who don't want to plug into the power socket.
There is often confusion with how these 'USB speakers' work. They are exactly the same as any other speakers, they have the same jack plug you would use on a ordinary set of speakers - they just draw power from the USB. No installation is required and they will work on any computer. The most basic set will give you a reasonable quality like you would have if they were mounted on the monitor. You can often get them really cheap off ebay or pay about £10 - £15 in most computer shops.