Natural Docs looks like a nice generator for code documentation. It's multi-language, with a more natural commenting style than Javadoc. It seems to be in fairly steady development, and has a slick homepage.
A quick browse of Wikepedia reveals a zillion documentation generators. This isn't really a surprise - once again the OSS ecosystem thoroughly fills a technological niche! Robodoc and Doxygen are other leading players. Wikipedia is (rightly) very neutral in its comparison. I'd be interested to learn if there is a reason to prefer one more than the others (say, from the point of view of wanting to support a new language).