Mike Cane found a video on Youtube showing what looks like a DIY ereader based on a BeagleBoard. It's running FBReader on a customized version of Linux. The screen is 4.3" (480x272 resolution).
I know it looks like a 1 of a kind kit, but it was actually assembled from commercially available BeagleBoard components. You can even buy this as. Retail is $423.61 (plus shipping).