One downside to the nook is the battery life. Supposedly this is better since the latest firmware update, but I'm not yet convinced. Also, they are quite a bit heavier and bulkier than the new kindles/sonys. This may be annoying since you'll be travelling.
The new Sonys are very nice--the screen on my 650 is very crisp and clear and the battery lasts 2-3 weeks with fairly regular reading. Downside to the Sonys is the price. If you do decide to go for a Sony--make sure you stay away from the 600/700/900. Those are the first gen touchscreens--and are nowhere near the 350/650/950 in readability.
The kindle would be a good choice--except it doesn't have ePub support.
I don't know much about it, but the kobo might be a good choice for you. It has a 6" screen, supports ePub, has a memory expansion slot. It has an e-ink display, but I'm pretty sure it doesn't have the new "pearl" screens that the Kindle and Sonys do.
Good luck!
dordale
