Recently acquired a pair of Creative T10 speakers for the Mac Mini and I have to say they are just excellent.

You can pick these up for £30 on Amazon but I got an as new pair locally, for £15 on Gumtree. Of course at this price you get a couple of fairly thin plastic boxes but buy them for the sound. Once I got the tone control set to something appealing and fed them a decent signal like HD audio from YouTube, I was most surprised. A really well integrated sound - surprisingly well controlled bass, reasonable depth and a very pleasant treble.

For non 'critical' internet listening you cannot go wrong.