I'm interested in producing feeds using Atom (the XML syndication format) and Java, but I'm not sure where to start.
Can anyone recommend libraries, tutorials etc. to get started?
Apache Abdera is your best bet - Apache Abdera
It contains client code for consuming Atom (and turning feeds, entries, collections into POJOs) - and it contains some base Atom server code for starting your own Atom Pub/Syndication server. The server code is a little clunky though, I wrote my own server and basically ignored most of the server code, just using their object model to parse/manipulate the Atom concepts.