One of the most famous mistakes is the so-called "Wicked Bible" that commands one "Thou Shalt Commit Adultery." It's a misprint of a 1611 KJV. One copy has been on display for a few years now. (source)
Generally speaking, if you ever look at the footnotes of an ancient text with multiple sources, you'll find that there are almost always "Other mss [read]" or some variant thereof. That indicates that some scribe wrote something different either intentionally or by mistake. Sometimes the obvious mistakes are omitted, sometimes not. Depends on the edition.
We were discussing just the other day about the 666 and 616 confusion in The Book of Revelation which helps identify the Beast as Nero.
But one problem you'll run into with many pre-modern documents is that spelling wasn't always standardized. The standardization of English had several efforts but were met with only moderate success. The American standardization of English did prove somewhat successful thanks to Noah Webster, things like the removal of u from color and always writing -er instead of -re. I daresay anything in English prior to the 18th century is prone to some spelling "errors." I mean, just pick up any Shakespeare or Chaucer.
And FWIW, Cambridge recently made an error in Ancient Greek signage regarding bicycle removal.
The US consitution actually has a few: the most well-known is Pennsylvania (disputed, but inconsistent in the document). There are a few other minor spelling "errors" because sometimes words are spelt in Queen's English, while somewhere else US English is used.
I remember the West Wing had a thing about a missing comma in the Constitution or something. Was that true?
Yes. Article from the National Archives that discusses various types of errors in the US Constitution: http://www.archives.gov/publications/prologue/2012/fall/const-errors.html