Here is a little thing I did on messaging
patterns for some folks at work. There is some async stuff down a ways. There is also a reference to
Enterprise Integration Patterns where thay have much more on messaging. If you don't want to get into JMS you won't really be doing messaging, but many of the concepts would apply do doing your own async work.
I don't think I know any other specific references on async callbacks. Event driven environments like Swing might be similar. I almost called my "subscriber" a "listener" in the diagram above. Swing listeners would give you some good background in handling events where the timing and sequence is out of your control.