Just found today that the United States National Archives have crystal-clear jpegs of the Constitution, Declaration of Independence, and bill of rights.
The Declaration of Independence in particular is astounding, because once it was written and signed it was made into an engraving, which (being acid- and fade-proof) is still 100% readable. You can see where the scribe made a couple typos which were subsequently corrected. Of interest to me was the cursive long s and the interesting use of rules between sentences to aid justification... Finally it's great to imagine from the signatures the jealousy John Hancock inspired: I can just see Ben Franklin trying to copy his swash, then giving up with a half-hearted scribble.