dead as a doornail - I’ve heard this all my life.
Somehow
dead as a rusty can
dead as a hammer
dead as a hairball
Doesn’t have the same zing to it. 
Who came up with dead as a doornail? What is a doornail? Is it literally a modern nail driven into a door? I’ve seen old houses where someone hung their robe from a nail. Is that nail a doornail?
From the Word Detective:
Many sayings like this catch on because of snazzy rhyming or alliteration. In this case the alliteration gives it a poetic ring.
Also note other similes that are adopted not because of their literal accuracy but rather they have a nice ring to it:
Cool as a cucumber–well, OK, a cucumber can be cool but hardly the coolest thing I can think of
Drunk as a skunk–I think “drunk as a redneck on five-cent beer night” works better
Fertile as a turtle–turtles aren’t more fertile than anything else
**
Naked as a jaybird**–no idea why this particular animal seems more naked than any other
[slight hijack]–No thread on door-nails would be complete without
Mr Dickens goes on to raise exactly the same question as the OP:
Mind! I don’t mean to say that I know, of my own knowledge, what there is particularly dead about a door-nail. I might have been inclined, myself, to regard a coffin-nail as the deadest piece of ironmongery in the trade. But the wisdom of our ancestors is in the simile; and my unhallowed hands shall not disturb it, or the Country’s done for. You will therefore permit me to repeat, emphatically, that Marley was as dead as a door-nail.
I understood from several sources that ‘dead as a doornail’ referred to the use of nails to attach doors with strap hinges way back when. The hinges were mounted on the outside of a home, wrought iron nails went all the way through the hinge and wall (or door), and then were not simply bent over once on the other side, but doubled over so that the nail was pushed back into the door in the opposite direction. This made it impossible to pull the nails out from the outside to break into a house. They nails were considered dead because a nail bent over once could be restraigtened for use again, but when bent over twice were considered useless thereafter. The reuse of nails was common, and wrought iron nails were valuable. According to a History Channel special on hardware stores, the blacksmith shop was the original hardware store, and smiths spent a lot of time making the most popular item, nails. They also claimed the value of nails was so great that old homes would be burned down so that the nails could be recovered from the ashes, and the primary reason for the development of general purpose screws was to secure modern jamb hinges that replaced the older strap hinges.
Just stepping in to add that this question comes up periodically. Here are two previous threads: Dead as a doornail and What is the origin of “Deader than a door nail?”. The second of these points out that Shakespeare used it in Henry VI.
Years ago, I heard “dead as a dodo” used occasionally. But, not recently.
Star Trek fans say “He’s Dead Jim” a reference to an over used line in the original series.
Thanks for the replies. 
I saw this thread, and knew that the Dope would not disappoint. Thank you, samclem et al.
And yet nobody here got the origin. It is another Shakespeare cliche. http://www.phrases.org.uk/meanings/phrases-sayings-shakespeare.html
Old Willy probably used doornail because it was alliterative and in meter.
“Clinching”, the process, a cut away view.
CMC fnord!
Your own link says that Shakespeare wasn’t the origin:
That predates Shakespeare’s use of it by more than 240 years.
Well count me wrong. I coulda sworn it was Henry VI, but wrong I am.
That quote, which was in the link, actually was from ca. 1375.
The 1350 cite in the OED is from
which was a list of all kinds of nails
Wait, that’s a 3 penny nail – way too small for a door.
<does the British money conversion>
So “three-penny nail” referred to the price for 100 of them? And the price was stable enough for a long enough time that the term got fixed in usage to where it’s survived after all these centuries of inflation?
What does the 2s represent there? The penny was used to designate the price for 100 nails in the 15th century. I would assume some nail producer standarized the unit around the nail size at some particular point in time based on their current prices. But the difference in price between the 14th and 15th centuries isn’t going to explain .6 pennies per 100 doornails if they have any relation to the standard sizes used today.
2s 6d, under the old British system, meant “two shillings sixpence”, or, since a shilling is 12 pence, a total of 30 pence. And 30 pence for 1000 nails would, of course, be thrupenny for 100.
The “penny measure” of nails represents the price of 100 of them in A.D. 1500. I didn’t worry about the inflation because I was making a JOKE.
