There a many, many, e-book reader devices available these days, and they're quickly becoming pretty affordable. The currently cheapest device in Germany (that I know of) is the TrekStor eBook Reader 3.0, model number EBR30-a, at 59.- Euros via Weltbild or Hugendubel.
The device has an 800x480 7" TFT (yep, no e-ink), 2100mAh battery, it can display PDFs, EPUB, and TXT files (and Adobe DRM crap, which I don't really care about), it has an accelerometer which allows for landscape/portrait switching, it can play MP3, OGG, WAV, and WMA audio files (headphone jack), it can display pictures (BMP, GIF, JPG, even PNG, though that's not mentioned in the vendor's specs), and it has 2GB internal storage for books/music/pictures. Uploading of (non-DRM) content is done by a simple file copy, it enumerates as a standard USB mass storage device with FAT filesystem. It's a relatively nice reader for the price, I've read a few PDFs (datasheets, presentations) on it in the subway/train while listening to music from the device and it's quite OK for my purposes. So much for the review part.
However, I didn't really buy it for reading books on it, I was more interested in taking it apart, of course ;-) My hope was that it would turn out to be a really cheap device running Linux/U-Boot which would be perfect for playing around with embedded Linux stuff. Unfortunately, I wasn't so lucky (it seems).
I've posted a few photos of the device and its hardware components on my flickr account and over at randomprojects.org, together with all the information I was able to find out so far. Here's a quick summary:
There are public datasheets for most of the hardware components (see randomprojects.org for links), but unfortunately the most important one (for the CPU) is not yet found/identified. I was told that the CPU/SoC is probably based on an ARM9 (ARM926EJ-S) core and the firmware running on it seems to be some uCos-based RTOS (not Linux, unfortunately).
So far I was not able to find out the vendor name or website of the "FI E200" CPU/SoC (let alone any datasheets), any hints would be highly appreciated. I checked arm.com: Processor Licensees, but the only two companies whose name starts with "F" having licensed an ARM9 core are Fujitsu and Freescale, which doesn't fit, I think?
I could (and probably will) check the PCB for RX/TX lines on an UART and/or JTAG pads (none are obviously labelled), and given that it's and ARM9 core there is a good chance that OpenOCD can be used and that a standard cross-gcc toolchain for ARM will work. However, that is all pretty pointless until it's clear which SoC exactly is used, and thus whether there is already Linux and/or U-Boot support for it and/or whether datasheets are available so that the respective code could be written. Without datasheets, this is going to be a pretty painful experience, not really worth investing much time, IMHO.
If anyone knows more about the vendor/device and respective datasheets, please let me know. Thanks!
Update 2012-04-19: I found the UART TX pin a while ago, a bootlog is available. The CPU and all other chips are also known now: The SoC is an Allwinner Technology F1 E200, the orientation sensor is a MEMSIC MXC6225XU.