There are a plethora of books out there to use as references, however, while MLA and Chicago pretty much remain the same from year to year, APA seems to change almost yearly. The APA guide sixth or seventh edition is the latest. There are websites out there that specialize in one or the other of the reference styles. Yes, punctuation rules are pretty much forever and don't change. The differences, quickly, between MLA and APA is in the way that the citations are references are arranged in the works cited/Resources/bibliography portion, as well as in text citations. MLA lists author's last name and the page number where the reference occured, whereas APA lists last name of the author and date of publication. There are varying rules regarding website citations so you'd have to refer to the website for those (they change yearly too).