We all know that someone with a doctorate is called a Doctor (or abbreviated as Dr.), is there a formal title for someone with a Masters degree? I've never heard someone refer to a person with a masters as "Master". I've also heard that Esquire is sometimes used as a formal title for someone with a masters, is this correct or is there another title?
In the United States there's no formal pre-nominal title held by individuals holding a Master's degree that I know of, so it's very unlike Dr. Xxxx that one holding a Ph.D., etc. might be addressed. In text, you would address such a person with a post-nominal suffix like M.A., MBA, etc. I'm sure the logic is different among specific types of degree, where Esq. for Esquire is a post-nominal suffix for those in the legal profession in the US. To give you an example, though: If I hold an M.Sc., you might refer to me as "Kendall, M.Sc." if you wanted to address me in an email or letter, but I would realistically expect Mr. Kendall or what have you face-to-face.
I should also add that courtesy titles like Esq. or Mr., and academic titles don't get used at the same time. Kendall, Esq. M.Sc. would be wrong, as would Mr. Kendall, M.Sc.!
A somewhat archaic title someone holding a Masters degree is "Magister". Similar to Doctor, it comes from a Latin word for teacher.
In the English speaking world, this title has essentially disappeared though, so would be met with incomprehension. In many other places Magisters degrees are conferred, but tend to be equivalent to doctorate, thus making use of the term even more inadvisable (but a fun thing to know about).
The official title is "Master of xxx" for someone who has attained a Master's degree in a given topic. I have also heard the phrase "Mistress of xxx" been used for a female; though I cannot speak to whether it is a traditional title. However, as others have said it is now customary to address someone with a master's or bachelor's degree with a post-nominal suffix rather than as a "master" or a "bachelor".
The merits of the title have evolved over time -- in the late middle ages, someone who had been granted the title of master was typically eligible to teach at a university. In addition, in those times it was considered more proper to refer to someone as a master if they had earned such a degree in a university. However, having a higher degree in those times was much less common than it is today.
It is worth noting that this question was asked on the English stack exchange board as well.