I’ve added to this post since I first wrote it. New stuff is in italics.
I bought an Archos Jukebox 20 gigabyte MP3 player a couple of years ago and have been enjoying it without any major problems. I bought it right around the time the iPod came out. Its primary advantage at the time was that you could get 20 GB of storage space for $300 whereas the iPods gave you 10 for $500.
On my birthday my girlfriend gave me a 20 GB iPod. It has some great advantages over the Archos. The best are that it looks much cooler and is smaller (much lighter). Apple did a great job with the iPod, giving it 32 MB of memory so that it could read ahead 20 minutes without having to spin the hard drive back up again (the Archos has 2 MB so it can read ahead about 2 minutes). They also used a tiny little hard drive and internal batteries with a much faster firewire connection to the PC. Also the accessories were much better, including the nice earbud headphones, small AC jack, and remote. The headphones for the Archos were so bad I had to buy replacements right away and even the AC adapter was a cause of concern since it got the unit very hot during recharging influencing me into buying a huge Radioshack adapter with “regulated” voltage.