I thought I’d never see a definitive answer to this one, but thanks to the brand-new Google NGrams Viewer, the facts are clear:
It is “another think coming,” and it has always been “another think coming.”
A lot of words and phrases (though not these) show a dip starting in 2000 or so. I wonder if the nature of the corpus changes at that point to include more words? You see the same effects with name frequencies — the frequency of any given name has been decreasing over the last twenty years, just because names are getting more and more widely distributed; the most popular names today take up a smaller share of namespace than much lower-ranked names did in the 1950s. A quick and dirty thing to check would be the entropy of the word distribution; is it going up with time?
Lots of good ngram examples on Tom Scocca’s blog, here and here.
Oh, and here’s the Four Shortstops:
Ripken, appropriately, is showing great staying power.
Quomodocumque 
Cool…
Any insight on the rise of the flabbergasted?
http://ngrams.googlelabs.com/graph?content=nonplussed, flabbergasted &year_start=1800&year_end=2000&corpus=0&smoothing=3
“He” occurs consistently about twice as often as “she” and yet with “him” and “her” it’s reversed!
But maybe “her” should also be paired with “his”, which wins.
[…] Ngrams: one more way to win an argument using Google (quomodocumque.wordpress.com) […]
If you put in a year, then for some reason the year it appeared the most seems to be consistently 4 years later.
Eggs Benedict is smoked by kippers, which, in turn, has recently been passed by crumpets.
Here’s a Facebook page we made to share interesting ngrams:
http://www.facebook.com/nteresting.ngrams