eigenclass.org is mostly Ruby stuff: code, information on the internals, news about the 1.9 branch, unusual hacks... I've tried to stay away from the most trivial things, so you won't find tutorials that rehash the basics of blocks, higher-order methods or modules (the set of things I consider basic is seemingly larger than for most people, though). I feel there's more than enough of that out there. More on that below.