Looking for a portable amp, preferably $100-200

I haven't the slightest clue about portable amps, but from what I'm seeing with audiophiles today, is that they have portable amps to go with their Mp3 players of choice. Can anybody refer me to a good range of products for sale? I can afford anything $200 and under. Ray Samuels Audio seems interesting, but kind of out of my price range; any thoughts?