I've used Archos, Pogo Ripflash
Both are hand held battery powered mp3 recorders.
The Archos has a built in hard disk with 10, 15 or 20 GB and will record in VBR mp3 at rates up to 192 KBPS. Some people have swapped in a 60 GB drive and the unit still works. The Archos supplied firmware is terrible, but there is a free open source replacement firmware called Rockbox, which is quite good.
The unit is about 3 by 4 inches and over an inch thick. It runs off 4 rechargeable AA batteries. It does a decent job, but it is a bit finicky, mechanically. You can expect at least 8 hours of operation from a fully charged set of batteries.
Don't use the built in mic. It picks up the disk drive spinning up.
To use the line in, you will need a battery box and pre-amp for an external mic. Archos makes one for about $40. A real good unit from Sound Professionals will run about $200. There's also a digital in jack. The LCD screen will display recording level.
The Pogo Ripflash is the size of two books of matches and weighs about as much. Ir runs on two AAA batteries and will do CBR up to 224 KBPS from an external source, 112 kbps from the internal mic. It uses Smart Media, and there's a slot that will hold an extra 128 MB. The unit comes with 128 - 256 MB internal depending on model. The first set of batteries lasted at least 10 hours.
The Ripflash Plus has both an internal mic and a speaker, and they aren't terrible. You can use the same type of external mic/battery box/preamp with the line in, but you'll have to guess at the level to set, as there is no level display on the LCD screen.
Both have USB for fast transfer of files to a PC. Archos uses Windows Explorer. Pogo has their own software.
One big difference:
Archos functions exactly like a hard disk. You can transfer files from and to your computer no matter where they came from.
Pogo Ripflash only allows you to upload files you have recorded on it. If you download a file to the unit, you can't upload it back again.