I'm not only talking about names that existed during the classical period, but also the standard Latinization of modern European names; for example hugo, hugonis is the standard medieval Latin rendering of "Hugh"; ioannes, ioannis for "John", and so on.
Is there some reference where I can find these standard Latin versions of common names?
I think English-Latin dictionaries are your best choice here. For instance, this dictionary has 6 pages of "Christian names" (and some surnames) in Latin. Other examples are pages 311-2 of this dictionary, and page 927 of this one. There is also a Wikipedia list (although it is sorted in Latin). Unfortunately this list has no references, so I would double check them with the lists above.
