The first Ogg-friendly music player I purchased was a Neuros II; this was late in 2004 and hardware support was fairly new as the Vorbis codec didn't reach 1.0 until 2002. Then, as now, the best place for information on Ogg-friendly devices was XiphWiki. I recall being quite impresssed with Neuros' willingness to open up the device specifications and embrace the Open Source community, unfortunately the device suffered from a number of design flaws that no amount of firmware hacking could ever resolve. Ultimately the combination of charging problems, a design plagued by awkwardness and bulk, and the manufacturer's shift to focus on newer devices doomed the Neuros II to my technology junk drawer.
The next portable Ogg player I bought, iRiver's IFP 899, had a number of laudable features. I like the small size since I generally want to listen to, rather than look at my music player, so it's usually stuck in a pocket. Not surprisingly, most of its bulk was to house the power supply: a single AA battery. I tried both rechargeable and disposable AA batteries but my cheap chinese rechargeables perform better in high drain devices. The disposables worked nicely, each battery was good for about 35 hours of playtime. Ogg support was limited (96-224kb/s) and a firmware update was required to mount the device as USB storage. The biggest downer was that the UMS firmware doesn't sort the files (or sorts by inode, if you prefer) so the tracks are played in the order by which they are transferred to the device. There are a few ways to work around this, but in the end it remains an annoying flaw and joins the other outcasts in my junk drawer.
The new product I referred to in part one is Cowon's iAUDIO U3. Like the other two players, the U3 uses flash storage, but it sports a full color screen and even plays tiny little pointless movies ;) It has an internal rechargeable battery but some checking has indicated that replacement does not require sending the unit back to the manufacturer. The U3, I'm happy to report, seems to meet or exceed my four basic requirements for a portable audio player, and I haven't even flashed the firmware.