Whewheew - I finally got a portable MP3 player. I chose the Archos Gmini 220 which has a 20GB drive:

I wanted one with a harddrive that does not make a difference between "data" and "music" like the iPod or the players from Rio do. At first I was fond about the iRiver H140 with its 40G harddrive. But there is no good solution to use it as an image tank, i.e. transferring files from Compact Flash cards to the harddrive directly, without a computer in between.
The Gmini 220 has a CF slot on one side and therefore manages this task natively. I suppose this was the final criterion... sorry iRiver, you lost. :-)

The major drawback with my new toy is that it cannot play ogg/vorbis files, like the players from iRiver can. However, this can be fixed:

find /mnt/gmini/Music -type f -name '*ogg' -exec ogg2mp3 "{}" \;

where ogg2mp3 is nothing else than:
#!/bin/sh
if [ -e "$1".mp3 ]; then
echo "already converted"
elif [ -e "$1".mp3tmp ]; then
echo "aha, aborted before..."
rm "$1".mp3tmp
oggdec -o - "$1" | lame - "$1".mp3tmp
mv "$1".mp3tmp "$1".mp3
else
echo "normal operation"
oggdec -o - "$1" | lame - "$1".mp3tmp
mv "$1".mp3tmp "$1".mp3
fi
rm "$1"

In addition, I already lobbied archos to support OGG in future versions of the firmware. And I intend to remind them from time to time, to do so...

I just tested it out and everything works to my satisfaction - I am just thinking if I should buy the remote control with the FM-radio as well..... I'll see.
Definitely I will have to buy better earphones - the ones that come with the player are horrible...