Actually, I recently had to dismantle and repair the Archos 20GB I had due to a manufacturing defect (they soldered the negative battery terminal on wrong - and it eventually caused it to quit...)
In any event, for the cost of an Archos 20GB MP3 player (and mine has always frozen within an hour of starting, even on the AC adapter) for the $213 minimum price I could find on Pricewatch, I could get an external 250GB USB2.0 hard disk drive, i.e. OVER TEN TIMES MORE STORAGE!
So, for a USB HDD, the Archos isn't very good. It's not all that great as an MP3 player, either. It needs its internal rechargeable batteries to work, and an AC adapter to be reliable.
The brand to shop for is unimportant. Shop for waranty, and failing that, buy an enclosure for $30, and put any IDE hard drive you like in it.
If you want VERY portable hard drives, then you could go for one of the MANY brands/types of USB2 notebook drives that draws its power from the USB bus (i.e. it DOES NOT NEED AN EXTERNAL 'wall wart' power supply). If you don't mind paying $200 for 20GB worth of storage, then you probably shouldn't mind paying $123.90 for 20GB worth of storage that
you don't need to drag around an extra power adapter for.
Go to
http://www.pricewatch.com, click on "Hard Drives" (under "Storage") and start shopping.
Anyway, the notebook drive type ones that draw from USB can still be very small, and convenient, but give you far bigger bang for the buck. One of the 1GB "pen drives" runs about $300, and you can get a 60GB of storage that fits in your palm or shirt pocket for $175.
(A search for "60GB adapter" turns up...)
http://www.isystor.com/poexusb20hi61.html
"40GB pocket" turns up a savings of about $20 for 2/3 the capacity... bad deal.
"80GB pocket" turns up an 80GB drive for $223.00 that doesn't require an external power solution other than the USB bus.
Words to look for are "Powerless" "No AC Adapter" "USB Powered", under any "nnGB Pocket " category.