Hey, with the wifi only Kindle being a nice option for those, like me, strapped for cash, I just wanted to share what I think is the best solution for offline wikipedia viewing.
http://www.en.wikipedia.org/wiki/Wikipedia:Books
Lets you dowload 'books' created by others (essentially collected articles), but the choice isn't amazing. You can however create your own books under the print/export option on the left hand side, and add whole catergories; unfortunately they're only avaliable as pdf's, but calibre can lend a hand with that.
Anyway enjoy