My main mobile reading tool is a satnav - a Navman iCN520, which is actually a PDA in disguise.
320x240 3.5in backlit touchscreen, SD (not SDHC) cards
It runs Win CE .Net 4.2 (with a lot of stuff removed to save space) and was unlocked to allow its full potential following instructions from here:
http://navmanunlocked.wikispaces.com/Unlock
I'm currently using an oldish (4.8 - win CE) version of mobipocket reader, after having tried MS Reader (yuk - slow, no control of fonts and layout), and hallireader (nice, but text only, and limited format support).
I can get at least 8 hours reading out of it on one charge with it clocked down to 100Mhz, and the screen is viewable in direct sunlight - useful as I've just been on holiday...
If you have a similar satnav and think its only good for driving it may be worth googling to see if it can be unlocked!