If you have a G4 tower with a processor faster than 500 MHz, or a new flat-panel iMac, your Mac has a built in amplifier (I believe it's either 16W or 20W, depending on the model). Normally this amp can only be used to power the special Apple speakers, but with this adapter you can hook up any standard pair of speakers:
http://www.griffintechnology.com/audio/prospeaker.html
Pretty cool for only $25
http://www.griffintechnology.com/audio/prospeaker.html
Pretty cool for only $25






