I recently got my hands on an Archos PMA400 (Pocket Media Assistant), a Linux based portable media player. The hardware of this device is really cool check it out: 30GB harddisk, WiFi, USB client, USB host and infrared (IrDA). The whole thing is powered by a Ti-OMAP processor and 64MB ram.
In my opinion the device really qualifies to be a true hacker Linux device, the USB host controller especially pushes this point! In general it allows one to connect any kind of USB device to the PMA, which is totally cool (I never saw something like this on any other mobile device). Just for fun I connected a keyboard and it worked immediately (makes life easer when examining the device through a console). Also my Bluetooth adapter got recognized, but the userspace applications are missing (which you can install your self with little hassle).
The device runs a 2.4.19 kernel and Qtopia 1.7 for the UI. Qtopia also provides a whole PIM suite which makes the device much more then a media player.
Archos also released an SDK and the source for the device, but as far as I know the boot loader only loads the original preinstalled and singed kernel image, so running your own kernel takes a little more then just replacing the kernel image.
Quite a few people all ready ported OpenZaurus software packages to the PMA400 (need to change the filesystem layout inside the packages). Just Google.
As soon as I have some valuable output I will post the results.