If you want more of a tablet and less of an e-reader...
The Android Pi project has a working build of gingerbread and an "unusable" build of ICS. You could probably combine that with a touchscreen monitor, there are some in the USB variety. By bundling it with a battery, such as a hydrogen fuel-cell model (with a USB port for charging) and putting it in a case, you might have some luck. If it worked, it would certainly be functional, akin to a mid-2010 or so low-end android tablet.
A monitor like this
might work for you, assuming the drivers are compatible.