Short of having the actual APA Style Manual in front of you, one of the best resources online is the APA formatting guide (Excelsior OWL), with sections on formatting both the paper and the references.
Along with bibliographic reference managers like Zotero, Mendeley, and EndNote, the Ebsco and ProQuest databases have their own "cite" option to generate APA-style references. There is also a citation generator within UC Library Search.