What is the official Roman Catholic Bible? If I want to buy a copy of the Bible, which version does one buy that would be the official Roman Catholic version?

It seems the Kings James version is the most popular, is that the one?

Will this contain both the New and Old Testament?
The Official Bible is the Vulgate, translated into Latin from (mainly) Greek by St. Jerome in the 4th Century after the canon was finally established.

The Council of Trent's Fourth Session defined the old Vulgate as authentic (source):


  Moreover, the same sacred and holy Synod,—considering that no small utility may accrue to the Church of God, if it be made known which out of all the Latin editions, now in circulation, of the sacred books, is to be held as authentic,—ordains and declares, that the said old and vulgate edition, which, by the lengthened usage of so many ages, has been approved of in the Church, be, in public lectures, disputations, sermons, and expositions, held as authentic; and that no one is to dare, or presume to reject it under any pretext whatever.


If you're looking for an English translation, any Bible with an imprimatur should be good.  I wrote another answer here a while ago about whether Catholics can read the NIV that might be of use to you.  The point is, Catholics should look to the Church for official interpretation no matter what the translation is.