KindleLinkWikipod installs a user-selectable portion -- or maybe all -- of Wikipedia into the Notes folder on any recent iPod; it does not require any new software (e.g. ipodlinux) to be installed!
Wikipod will be stunning to the many people who are not keen on messing with their iPod's OS, but who would like to carry a Healthy Portion Of World Knowledge in 1.46 cubic inches. User specifies a size limit, say 10 MB, and a starting word, and Wikipod spiders from there, installing a subset of Wikipedia around your favorite topic. Article hyperlinks work quickly (on my nano, at least), and a moderate-sized topic listing is suprisingly browsable via scrollwheel.(The full text of Wikipedia these days is about 1.1 GB, but not sure yet if Wikipedia connectivity is such that the current script can get the entire thing to an iPod)
Wikipod works on a standard iPod; it does not require ipodlinux to be installed; the related (Encyclopodia, which was reported in Boing Boing back in Feb. 2006, does require ipodlinux to be installed).
A a tiny test, I tried just 10 MB starting from "Essence" -- my nano soon became a teensy creditable guide to Existentialist philosophy and related movements. Darn thing didn't pick up "nominalism"; I'll try for 100 MB of Essence next.
Minor cons: Wikipod doesn't install graphics, makes the occasional mistake with pages (it's new; fixes may come soon). Big pros: overall works shockingly well with the existing Apple Notes hyperlink interface. I wouldn't read too many novels on my nano screen, but a reference like Wikipeda is perfect for it!