Samuel Johnson - A Dictionary of the English Language (1755)
Archive.org direct link (8th edition, volume 1)
Archive.org direct link (8th edition, volume 2)
Open Library main page (with links to various editions)
Digital edition (see below)
This is the third of The Guardian's Top 10 Dictionaries. Johnson's dictionary wasn't just a landmark reference work but was also so readable that selections have been reprinted many times. (A Penguin may be the easiest to find - it's still in print. I have one from the 70s that was half of a two-volume selected works.) Johnson spent years on it (while also finding the time to edit a major edition of Shakespeare) and pulled together various approaches to create a dictionary that was thorough and accurate though not always disinterested. (He attacked the Scots in one entry.)
I gave links to the 8th edition purely because that scan seemed most readable though I didn't look at all. The Open Library link lists many others.
The digital edition link above goes to a very nice site with much background information and links. Part of that project is to transcribe the entire first edition (at 9% as of this writing). It also has a very clean scan of the first edition but that's somewhat hard to find - go to Page View and then you can choose from there.
There are several books about the dictionary though the one that most interests me is Jack Lynch & Anne McDermott's Anniversary Essays on Johnson's Dictionary (2005), mainly because it's not narrative but focuses on specific topics such as the "mythology" of the dictionary, use of references, its typography, legal issues, political implications and most intriguingly "hidden quarto editions".