I had one of the first Altec portable iPod speakers, put many miles on it and really liked it. A speaker wire finally broke on it and after shopping around I replaced it with this:
http://www.logitech.com/index.cfm/speakersaudio/ipod_mp3speakers/devices/4320&cl=us,en
Really good sound, works with all iPods (including my iPhone 3G, I've gone about 10,000 driving miles with this one. 5 stars.